Basic Electrical Engineering MCQs

Contents

- 1 No current flows between two charged bodies when they have same
- 2 Electric current is due to the flow of
- 3 Temperature coefficient of resistance for semi-conductors is
- 4 Resistance of a straight conductor depends on
- 5 The diameter of an atom is about
- 6 Voltage drop across a 2 kW Electric Heater
- 7 Which of following is an example of non-ohmic resistance
- 8 A substance having number of valence electrons more than 4 is usually
- 9 With rise in temperature, the specific resistance of metallic conductor _________
- 10 The SI unit of conductivity is
- 11 With an increase in temperature, the resistance decreases in case of
- 12 The most suitable material for making connecting wires is
- 13 Ampere-second is the unit of
- 14 In case of liquids, Ohm’s law is
- 15 The electrons in the last orbit of an atom are known as
- 16 Electric current is a
- 17 The value of temperature coefficient of resistance depends on
- 18 1 cm^3 of copper at room temperature has about
- 19 A kettle is rated 230 V, 20 kW AC. The value 230 V is
- 20 For same peak value which of the following wave will have the highest RMS value
- 21 Which of following element has unity power factor
- 22 Which of the following is correct regarding the time period of a waveform
- 23 The voltage level of domestic supply at our homes is 230 V. The figure 230 is
- 24 A substance having number of valence electrons equal to 4 is usually
- 25 Constantan wire is used for making standard resistor since it has
- 26 The specific resistance of material of wire depends on
- 27 Electric current in liquids is due to flow of
- 28 An electron is moving in cirlce of radius 4.5*10^-11 m at a frequency of 5.28*10^15 revolutions per second. The equivalent current is approximately
- 29 If a piece of wire is melted and recast to half of its original length, the new resistance is
- 30 The resistance of human body is about:
- 31 A current flow of 10 A for 1 hour will transfer how much charge
- 32 The thermal speed of electrons is of the order of
- 33 Due to drop of current by 3%, the percentage by which incandescence of lamp decreases is
- 34 As temperature of metallic resistor is increased, the product of its resistivity and conductivity
- 35 A potential difference of 6 V is applied across a conductor that has resistance 3 Ω. The number of electrons flowing in 1s are
- 36 The specific resistance of material that is 3 m long and has 3 m^2 area of cross and having resistance value 1.2 * 10^-8 ohms is
- 37 A resistor R1 dissipates certain amount of power ‘P’ when it is connected to a power source. Another resistor R2 is connected in series to R1. The power dissipated by R1:
- 38 Yellow Violet Orange Silver will have resistance
- 39 Certain length of wire has a resistance of 6 ohms. What is the value of resistance of wire that is three times long and having two times the cross-sectional area
- 40 A resistor having color coding Brown Black Red
- 41 A solid cube of silver has mass 50 g. Considering density of silver 10.5 g/cm³ and resistivity to be 0.0000016 Ωcm. The resistance between two opposite faces of cube will be
- 42 Temperature coefficient of resistance of Eureka is
- 43 The mass of a proton is how many times the mass of electron
- 44 A substance having number of valence electrons less than 4 is usually
- 45 Conductivity is reciprocal of
- 46 The specific resistance of certain wire that is 1.5 m long, has 0.5 mm diamter, and having a resistance 5 will be
- 47 The electric power dissipated in a resistor in terms of its conductance G and voltage V across it is mathematically expressed in the form
- 48 The SI unit of conductivity is
- 49 Heat produced in conductor depends
- 50 The energy consumed in kWh when 10, 20 W lamps are operated for 10 hours per day in November is
- 51 A resistor coil of 120 Ω is immersed in 42 kg of water. If a steady current of 7 A is made to flow through the coil, the rise temperature of water per minute is
- 52 Certain motor when operated for 45 minutes consumes 0.8 kWh of energy. During that time, the total energy loss is 300000 J. The total joules of work performed in 45 minutes are
- 53 Two electric lamps, each of 50 W are connected in parallel. The power consumed by combination is
- 54 The time required for 2 kW heater for raising temperature of 10 litres of water through 10°C is
- 55 A heater coil rated at 1200 W, 220 V is connected to 100 V line. The power consumed is
- 56 A 8°C rise in temperature is observed in a conductor by passing current. When current is doubled, the rise in temperature will be
- 57 An electric heater, kettle, and oven are all rated at 1 kW, 230 V. Which of them has highest resistance
- 58 Certain tap supplies water at 20°C. A man takes 1 liter of water per minute at 39°C from geyser. The power of geyser is (Consider efficient to be 100%
- 59 The heat produced (in k cals) in resistance R ohms when a current I amperes flow though it for t seconds is given be
- 60 An electric fan and electric kettle are marked as 200 W, 220 V and 1000 W, 220 V The resistance of kettle is
- 61 The total power supplied to an engine that drives an electric generator is 50 kW. The generator delivers 15 A to load of 100 Ω. The efficiency of system is
- 62 The utility company supplies power at 230 V. In a house having 11 bulbs of power rating 100 W the fuse rating should be:
- 63 A constant voltage is applied across ends of conductor. The heat produced is
- 64 The 1 kHz signal has a period of 1 ms
- 65 The average value of a sine wave is 0.707 times the peak value
- 66 Periodic waveform is characterized by a repetition at fixed time intervals
- 67 The unit of frequency is the HERTZ
- 68 A signal having a 400 µs period has a frequency of
- 69 Electric current flowing through the circuit produces
- 70 The number of electrons in the outer most orbit of carbon atom is
- 71 All good conductors possess high
- 72 A glass rod when rubbed with silk cloth is charged since
- 73 When one leg of parallel circuit is opened out the total current will
- 74 Which of following can have negative temperature coefficient
- 75 A 40 W bulb is connected in series with a room heater. If now 40 W bulb is replaced by 100 W bulb, the output of heater will
- 76 The correct statement defining the semiconductor materials is
- 77 The property of a conductor because of which it passes current is known as
- 78 In case of direct current
- 79 The resistance of a conductor varies inversely with
- 80 Two bulbs of 500 W and 200 W rated at 250 V will have a resistance ratio as
- 81 A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms respectively. The current in each branch is
- 82 An electric filament bulb can be worked from
- 83 The substances that have a large number of free electrons and offer a low resistance are known as
- 84 You have to replace 1500 ohms resistor in radio. You have no 1500 Ω resistor but have several 1000 Ω ones which you would connect
- 85 Voltage dependent resistors are generally made from
- 86 The closed switch has a resistance of
- 87 When electric current passes through a bucket full of water, lot of bubbling is observed. This suggests that the type of supply is
- 88 An open resistor, when checked with an ohmmeter reads
- 89 The conductance of an 8 ohm resistance is
- 90 The atomic number is defined as the number of neutrons in the nucleus
- 91 Materials that do not allow current under normal conditions is
- 92 Electrons in the outer orbit are named
- 93 The current in a given circuit should not exceed 24 A. The recommended fuse should be
- 94 A voltmeter is connected across the current path
- 95 Which of the following is not an energy source
- 96 Materials with lots of free electrons are identified as
- 97 A wiper is the sliding contact in a
- 98 An ammeter is connected across the current path
- 99 A crystal diode uses which characteristic for rectification
- 100 The designation rms means repetitions measured per second
- 101 A ramp is the type of waveform that is characterized by a non-linear increase or decrease in voltage or current.
- 102 A phasor signifies
- 103 A significant constraint of a crystal oscillator is

## No current flows between two charged bodies when they have same

No current flows between two charged bodies when they have same

- Charge
- Capacity
- Potential
- None of the above

Correct answer: 3. Potential

Explanation: No current flows between two charged bodies when they have the same potential. Current flow is driven by a potential difference (voltage difference) between two points. When two bodies have the same electrical potential, there is no driving force to cause the movement of charge (current) between them. Even if the bodies have different charges or different capacities (capacitances), as long as their potentials are the same, no current will flow.

## Electric current is due to the flow of

Electric current is due to the flow of

- Positive charges only
- Negative charges only
- Both of above
- Neutral particles only

Correct answer: 3. Both of above

Explanation: Electric current can be caused by the flow of both positive and negative charges. In metals, it’s typically electrons (negative charges) that move, while in electrolytes and some semiconductors, positive ions or “holes” (positive charge carriers) also contribute to current. Neutral particles, which carry no charge, do not contribute to electric current.

## Temperature coefficient of resistance for semi-conductors is

Temperature coefficient of resistance for semi-conductors is:

- Zero
- Positive
- Negative
- None of the above

Correct answer: 3. Negative

## Resistance of a straight conductor depends on

The resistance of a straight conductor depends on all of below mentioned with the exception of:

- Temperature
- Shape of cross-section
- Material
- Cross-sectional area

Correct answer: 2. Shape of cross-section

Explanation: The shape of the cross-section (be it circular, square, etc.) does not directly affect the resistance; rather, it is the total cross-sectional area that matters.

## The diameter of an atom is about

The diameter of an atom is about:

- 10
^{-2}m - 10
^{-5}m - 10
^{-10}m - 10
^{-20}m

Correct answer: 3. 10^{-10} m

Explanation: The diameter of an atom typically ranges from about 0.1 nanometers (nm) to a few nanometers. One nanometer (1 nm) is equivalent to 10^{-9} meters. Therefore, 0.1 nm is equal to 0.1 x 10^{-9} meters, or 10^{-10} meters.

## Voltage drop across a 2 kW Electric Heater

The voltage drop across a 2 kW electric heater whose resistance when hot is 80 Ω

- 2 V
- 20 V
- 200 V
- 400 V

Correct answer: 4. 400 V

Explanation: V = √(P* R) = 400 V

## Which of following is an example of non-ohmic resistance

Which of following is an example of non-ohmic resistance:

- Carbon resistance
- Copper wire
- Aluminum wire
- Tungsten wire

Correct answer: 1. Carbon resistance

Explanation: Carbon resistors or devices like carbon-filled composites can exhibit non-linear I-V characteristics, especially under different conditions and compositions. The resistance of such materials can change depending on the temperature or the amount of current passing through them. Carbon filaments, particularly in their usage in older light bulb technologies, can exhibit non-linear properties where resistance increases with increasing temperature caused by the current.

## A substance having number of valence electrons more than 4 is usually

A substance having number of valence electrons more than 4 is usually:

- An insulator
- A semiconductor
- A conductor
- None of the above

Correct answer: 1. An insulator

## With rise in temperature, the specific resistance of metallic conductor _________

With rise in temperature, the specific resistance of metallic conductor _________

- Increases
- Decreases
- Remains the constant
- None of these

Correct answer: 1. Increases

## The SI unit of conductivity is

The SI unit of conductivity is:

- mho/m
- mho-m
- ohm-m
- ohm/m

Correct answer: 1. mho/m

## With an increase in temperature, the resistance decreases in case of

With an increase in temperature, the resistance decreases in case of:

- Copper
- Silver
- Carbon
- None of these

Correct answer: 3. Carbon

## The most suitable material for making connecting wires is

The most suitable material for making connecting wires is:

- Nichrome
- Copper
- Constantan
- Any of above

Correct answer: 2. Copper

## Ampere-second is the unit of

Ampere-second is the unit of:

- EMF
- Energy
- Charge
- Power

Correct answer: 3. Charge

## In case of liquids, Ohm’s law is

In the case of liquids, Ohm’s law is:

- Partially obeyed
- Fully obeyed
- Not obeyed at all
- None of these

Correct answer: 2. Fully obeyed

## The electrons in the last orbit of an atom are known as

The electrons in the last orbit of an atom are known as:

- Free electrons
- Valence electrons
- Bound electrons
- Thermionic electrons

Correct answer: 2. Valence electrons

## Electric current is a

Electric current is a:

- Vector quantity
- Scalar quantity
- Any of above
- None of above

Correct answer: 2. Scalar quantity

## The value of temperature coefficient of resistance depends on

The value of temperature coefficient of resistance depends on:

- Materials cross sectional area
- Volume of material
- Length of material
- Nature of material

Correct answer: 4. Nature of material

## 1 cm^3 of copper at room temperature has about

1 cm^3 of copper at room temperature has about:

- 1000 free electrons
- 30 x 10^10 free electrons
- 2 x 10^5 free electrons

Correct answer: 4. 8.5 x 10^22 free electrons

## A kettle is rated 230 V, 20 kW AC. The value 230 V is

A kettle is rated 230 V, 20 kW AC. The value 230 V is:

- Average Voltage
- Peak Voltage
- RMS Voltage
- None of the above

Correct answer: 3. RMS voltage

## For same peak value which of the following wave will have the highest RMS value

For same peak value which of the following wave will have the highest RMS value:

- Triangular wave
- Sine wave
- Square wave
- Half wave rectified sine wave

Correct answer: 3. Square wave

## Which of following element has unity power factor

Which of the following element has unity power factor:

- Inductance
- Capacitance
- Resistance
- Both 1 and 2

Correct answer: 3. Resistance

## Which of the following is correct regarding the time period of a waveform

Which of the following is correct regarding the time period of a waveform:

- It is same as frequency
- It is expressed in amperes
- It is defined as the time required to complete one cycle
- None of these

Correct answer: 3. It is defined as the time required to complete one cycle

## The voltage level of domestic supply at our homes is 230 V. The figure 230 is

The voltage level of domestic supply at our homes is 230 V. The figure 230 is

- Mean value
- Peak value
- RMS Value
- Average value

Correct answer: 3. RMS value

## A substance having number of valence electrons equal to 4 is usually

A substance having number of valence electrons equal to 4 is usually

- An insulator
- A semiconductor
- A conductor
- None of the above

Correct answer: 2. A semiconductor

## Constantan wire is used for making standard resistor since it has

Constantan wire is used for making standard resistor since it has:

- High specific resistance
- Low specific resistance
- High melting point
- Negligibly small temperature coefficient of resistance

Correct answer: 4. Negligibly small temperature coefficient of resistance

## The specific resistance of material of wire depends on

The specific resistance of material of wire depends on:

- Mass
- Length
- Area of cross-section
- None of these

Correct answer: 4. None of these

Explanation: Electrical resistivity also known as specific electrical resistance or volume resistivity is a fundamental property of a material that measures how strongly it resists electric current. The specific resistance of material of wire depends on the material from which it is fabricated and it doesn’t depends on the mass, length or area of cross-section of material.

## Electric current in liquids is due to flow of

Electric current in liquids is due to flow of:

- Electrons
- Positive ions
- Negative ions
- 2 and 3

Correct answer: 4. 2 and 3

## An electron is moving in cirlce of radius 4.5*10^-11 m at a frequency of 5.28*10^15 revolutions per second. The equivalent current is approximately

An electron is moving in cirlce of radius 4.5*10^-11 m at a frequency of 5.28*10^15 revolutions per second. The equivalent current is approximately:

- 4.2 * 10^-4 A
- 2.3 * 10^-4 A
- 5.86 * 10^-4 A
- 8.45 * 10^-4 A

Correct answer: 4. 8.45 * 10^-4 A

Solution:

Current = Charge/Time period = Charge * Frequency

=1.6810^-19 * 5.28*10^15 = 8.45 * 10^-4 A

The drift velocity of free electrons is of the roder:

- 1 m/s
- 10^-3 m/s
- 10^-5 m/s
- 10^-9 m/s

Correct answer: 3. 10^-5 m/s

## If a piece of wire is melted and recast to half of its original length, the new resistance is

If a piece of wire is melted and recast to half of its original length, the new resistance is:

- R
- R/2
- R/4
- 2R

Correct answer: 3. R/4

Explanation:

Suppose R = ρl/A is original resistance

And R’ = ρl’/A’ is new resistance

Since volume of wire remains same

lA = l’A’

A/A’ = l’/l

l’ = 0.5l

Now A/A’ = l’/l = 0.5 = ½

R’R = l’/l * A/A’ = ½ * ½ = ¼

R’ = R/4

## The resistance of human body is about:

The resistance of human body is about:

- 1 Ω
- 10 Ω
- 100 Ω
- 1000 Ω

Correct answer: 4. 1000 Ω

## A current flow of 10 A for 1 hour will transfer how much charge

A current flow of 10 A for 1 hour will transfer how much charge:

- 3.8 * 10^3 C
- 2.2 * 10^3 C
- 1.5 * 10^2 C
- 3.6 * 10^4 C

Correct answer: 4. 3.6 * 10^4 C

Solution: q = It = 10 A * 3600 s = 36000 As = 3.6 * 10^4 C

## The thermal speed of electrons is of the order of

The thermal speed of electrons is of the order of

- 10^-3 m/s
- 10^6 m/s
- 10^8 m/s
- None of these

Correct answer: 2. 10^6 m/s

## Due to drop of current by 3%, the percentage by which incandescence of lamp decreases is

Due to drop of current by 3%, the percentage by which incandescence of lamp decreases is:

- 3%
- 6%
- 9%
- 12%

Correct answer: 2. 6%

Explanation:

P = I²R or ΔP = 2I(ΔI)R

ΔP/P = 2ΔI/I = 2 * 3% = 6%

## As temperature of metallic resistor is increased, the product of its resistivity and conductivity

As temperature of metallic resistor is increased, the product of its resistivity and conductivity:

- Increases
- Decreases
- Remains constant
- May increase or decrease

Correct answer: 3. Remains constant

## A potential difference of 6 V is applied across a conductor that has resistance 3 Ω. The number of electrons flowing in 1s are

A potential difference of 6 V is applied across a conductor that has resistance 3 Ω. The number of electrons flowing in 1s are:

- 1.07 * 10^19
- 1.21 * 10^19
- 1.25 * 10^19
- 1.39 * 10^19

Correct answer: 3. 1.25 * 10^19

Explanation: Solution:

I = q/t = ne/t or n = It/e

n = 2 * 1 / (1.6*10^-19 C) = 1.25 * 10^19

## The specific resistance of material that is 3 m long and has 3 m^2 area of cross and having resistance value 1.2 * 10^-8 ohms is

The specific resistance of material that is 3 m long and has 3 m^2 area of cross and having resistance value 1.2 * 10^-8 ohms is:

- 1.2 * 10^-8 ohms
- 1.4 * 10^-8 ohms
- 2.38 * 10^-8 ohms
- 4.4 * 10^-8 ohms

Correct answer: 1. 1.2 * 10^-8 ohms

A resistor R1 dissipates certain amount of power ‘P’ when it is connected to a power source. Another resistor R2 is connected in series to R1. The power dissipated by R1

## A resistor R1 dissipates certain amount of power ‘P’ when it is connected to a power source. Another resistor R2 is connected in series to R1. The power dissipated by R1:

- Increases
- Decreases
- Will remain the same
- None of above

Correct answer: 2. Decreases

A resistor having color coding:

## Yellow Violet Orange Silver will have resistance

Yellow Violet Orange Silver will have resistance:

- 4.7 kΩ ± 10%
- 47 kΩ ± 10%
- 2.7 kΩ ± 10%
- 27 kΩ ± 10%

Correct answer: 2. 47 kΩ ± 10%

Explanation:

Yellow, Violet = 47

Orange = 10^3

Silver = ±10% tolerance

## Certain length of wire has a resistance of 6 ohms. What is the value of resistance of wire that is three times long and having two times the cross-sectional area

Certain length of wire has a resistance of 6 ohms. What is the value of resistance of wire that is three times long and having two times the cross-sectional area:

- 1 ohm
- 4 ohm
- 9 ohm
- 12 ohm

Correct answer: 3. 9 ohm

Solution:

R1 = ρ * l1 /a1

R2 = ρ * l2 /a2

R2 / R1 = (l2 / a2) * (a1 / l1)

R2 / R1 = (3l/2a) * (a/l) = 3/2 = 1.5

R2/R1 = 1.5

R2 = 1.5 * 6 = 9 ohms

## A resistor having color coding Brown Black Red

A resistor having color coding:

Brown Black Red will have resistance:

- 1 kΩ ± 10%
- 1 kΩ ± 20%
- 2 kΩ ± 10%
- 2 kΩ ± 20%

Correct answer: 2. 1 kΩ ± 20%

Brown, Black = 10

Red = 10^2

None = ±20%

## A solid cube of silver has mass 50 g. Considering density of silver 10.5 g/cm³ and resistivity to be 0.0000016 Ωcm. The resistance between two opposite faces of cube will be

A solid cube of silver has mass 50 g. Considering density of silver 10.5 g/cm³ and resistivity to be 0.0000016 Ωcm. The resistance between two opposite faces of cube will be:

- 3.29 * 10^-7 Ω
- 5.42 * 10^-7 Ω
- 9.51 * 10^-7 Ω
- None of these

Correct answer: 3. 9.51 * 10^-7 Ω

Solution:

Volume of cube = Mass/Density = 50/10.5 = 4.76 cm³

Each side of cube =4.76190476190476^1/3 = 1.68 cm

R = ρl/A = 9.51*10^-7 Ω

## Temperature coefficient of resistance of Eureka is

Temperature coefficient of resistance of Eureka is:

- Positive
- Negative
- Zero
- None of these

Correct answer: 1. Positive

## The mass of a proton is how many times the mass of electron

The mass of a proton is how many times the mass of electron.

- 1 time (is equal to)
- 3 times less than
- 400 times
- About 1837 times

Correct answer: 4. About 1837 times

## A substance having number of valence electrons less than 4 is usually

A substance having number of valence electrons less than 4 is usually

- An insulator
- A semiconductor
- A conductor
- None of the above

Correct answer: 3. A conductor

## Conductivity is reciprocal of

Conductivity is reciprocal of:

- Resistance
- Current density
- Resistivity
- None of these

Correct answer: 3. Resistivity

## The specific resistance of certain wire that is 1.5 m long, has 0.5 mm diamter, and having a resistance 5 will be

The specific resistance of certain wire that is 1.5 m long, has 0.5 mm diamter, and having a resistance 5 will be:

- 65 * 10^-8 Ω-m
- 23 * 10^-8 Ω-m
- 37 * 10^-8 Ω-m
- 44 * 10^-8 Ω-m

Correct answer: 1. 65 * 10^-8 Ω-m

Solution:

Area = πr² = π(d/2)² = 1.963E-07

R = ρl/A OR ρ = RA/l

ρ = 5 * 1.963E-07 / 1.5 = 6.54 * 10^-07 Ω-m = 65 * 10^-8 Ω-m

## The electric power dissipated in a resistor in terms of its conductance G and voltage V across it is mathematically expressed in the form

The electric power dissipated in a resistor in terms of its conductance G and voltage V across it is mathematically expressed in the form:

- V²G
- V²/G
- GV²
- G/V²

Correct answer: 1. V²G

Explanation:

Power dissipated (P) = V²/R = V²G

## The SI unit of conductivity is

The SI unit of conductivity is:

- mho/m
- mho-m
- ohm-m
- ohm/m

Correct answer: 1. mho/m

## Heat produced in conductor depends

Heat produced in conductor depends:

- Directly on time
- Inversely on time
- Both of these
- None of these

Correct answer: 1. Directly on time

## The energy consumed in kWh when 10, 20 W lamps are operated for 10 hours per day in November is

The energy consumed in kWh when 10, 20 W lamps are operated for 10 hours per day in November is:

- 15 kWh
- 30 kWh
- 60 KWh
- 120 kWh

Correct answer: 3. 60 KWh

Solution:

Watts consumed by 10 lamps = 10 * 20 = 200 W

When operated for 10 hours = 2000 wh

For 30 days of November = 2000 * 30 = 60000 Wh = 60 kWh

## A resistor coil of 120 Ω is immersed in 42 kg of water. If a steady current of 7 A is made to flow through the coil, the rise temperature of water per minute is

A resistor coil of 120 Ω is immersed in 42 kg of water. If a steady current of 7 A is made to flow through the coil, the rise temperature of water per minute is:

- 1°C
- 2°C
- 3°C
- 4°C

Correct answer: 2. 2°C

Solution:

Heat produced per minute (H) = I² Rt/J = {(7)² * 120 * 60 = 84000 cal

From formula

H = ms θ or θ = H/ms = 84000/(42 * 1000 * 1) = 2°C

## Certain motor when operated for 45 minutes consumes 0.8 kWh of energy. During that time, the total energy loss is 300000 J. The total joules of work performed in 45 minutes are

Certain motor when operated for 45 minutes consumes 0.8 kWh of energy. During that time, the total energy loss is 300000 J. The total joules of work performed in 45 minutes are:

- 1130000 J
- 1920000 J
- 2580000 J
- 3220000 J

Correct answer: 3. 2580000 J

Solution:

Motor input = 0.8 kWh = 0.8 * 36 * 10^5 J = 2880000 J

———–

Motor output = Input – Loss = 2880000 – 300000 = 2580000 J

## Two electric lamps, each of 50 W are connected in parallel. The power consumed by combination is

Two electric lamps, each of 50 W are connected in parallel. The power consumed by combination is:

- 25 W
- 50 W
- 100 W
- None of these

Correct answer: 3. 100 W

Explanation:

PT = P1 + P2 = 50 W + 50 W = 100 W

## The time required for 2 kW heater for raising temperature of 10 litres of water through 10°C is

The time required for 2 kW heater for raising temperature of 10 litres of water through 10°C is:

- 185 s
- 210 s
- 420 s
- 520 s

Correct answer: 2. 210 s

Solution:

From equation

m * S * T = P * t

Where

m = mass in gram = 10 * 1000 = 10000 gram

—————-

T = Temperature difference = 10°C

S = Specific heat = Energy required in joules to raise temp of 1 gram of mass by 1 degree celsiuc.

In case of water S = 4.186 joules/gram/°C

P = Power of heater = 2 kW = 2000 watt = 2000 joules/sec

t = time is second

—————-

t = (m*S*t)/P = (10000 * 4.186 * 10)/1000 = 210 sec

## A heater coil rated at 1200 W, 220 V is connected to 100 V line. The power consumed is

A heater coil rated at 1200 W, 220 V is connected to 100 V line. The power consumed is:

- 139.22 W
- 247.9 W
- 315.4 W
- 448.9 W

Correct answer: 2. 247.9 W

Solution:

R = V²/P = 220²/1200 = 40.3 Ω

Power consumed at 100 V = (100)²/40.33 = 247.9 W

## A 8°C rise in temperature is observed in a conductor by passing current. When current is doubled, the rise in temperature will be

A 8°C rise in temperature is observed in a conductor by passing current. When current is doubled, the rise in temperature will be:

- 8°C
- 16°C
- 32°C
- 64°C

Correct answer: 3. 32°C

Solution:

From equation: H ∝ I²

———————-

H2/H1 = (2I/I)² = 4

———————-

Now θ ∝ H

θ2/θ1 = H2/H1 = 4

θ2 = 4θ1 = 4 * 8 = 32°C

## An electric heater, kettle, and oven are all rated at 1 kW, 230 V. Which of them has highest resistance

An electric heater, kettle, and oven are all rated at 1 kW, 230 V. Which of them has highest resistance:

- Heater
- Kettle
- Oven
- All have equal resistance

Correct answer: 4. All have equal resistance

Explanation: From formula R = V²/P, since all have same voltage and power ratings, all will have same resistance.

## Certain tap supplies water at 20°C. A man takes 1 liter of water per minute at 39°C from geyser. The power of geyser is (Consider efficient to be 100%

Certain tap supplies water at 20°C. A man takes 1 liter of water per minute at 39°C from geyser. The power of geyser is (Consider efficient to be 100%:

- 985 W
- 1330 W
- 1485 W
- 1965 W

Correct answer: 2. 1330 W

Solution:

Heat output of device in joules per second is the power of device.

Power of geyser = mc θ * 4.2 joules.sec = 1000/ * 1 * (39 – 20 ) = 1330 W

## The heat produced (in k cals) in resistance R ohms when a current I amperes flow though it for t seconds is given be

The heat produced (in k cals) in resistance R ohms when a current I amperes flow though it for t seconds is given be:

- I²Rt
- I²Rt/5
- I²Rt * (4.2*10^3)
- I²Rt/(4.2*10^3)

Correct answer: 4. I²Rt/(4.2*10^3)

## An electric fan and electric kettle are marked as 200 W, 220 V and 1000 W, 220 V The resistance of kettle is

An electric fan and electric kettle are marked as 200 W, 220 V and 1000 W, 220 V The resistance of kettle is:

- Less than fan
- More than fan
- Same as fan
- Insufficient data

Correct answer: 1. Less than fan

Solution:

From formula R = V²/P

Resistance of fan = 220^2/200 = 242 ohms

Resistance of kettle = 220^2/1000 = 48.4 ohms

## The total power supplied to an engine that drives an electric generator is 50 kW. The generator delivers 15 A to load of 100 Ω. The efficiency of system is

The total power supplied to an engine that drives an electric generator is 50 kW. The generator delivers 15 A to load of 100 Ω. The efficiency of system is:

- 0.2
- 0.38
- 0.45
- 0.92

Correct answer: 3. 0.45

Solution:

Input to system = 50 kW = 50000 W

Output of system = I²R = 15² * 100 = 22500 W

——————–

System efficiency (η) = Output/Input = 22500/50000 = 0.45

## The utility company supplies power at 230 V. In a house having 11 bulbs of power rating 100 W the fuse rating should be:

The utility company supplies power at 230 V. In a house having 11 bulbs of power rating 100 W the fuse rating should be:

- 2.22 A
- 4.78 A
- 5.69 A
- 7.22 A

Correct answer: 2. 4.78 A

Solution:

P = VI

or I = P/V = 11 * 100/230 = 4.78 A

## A constant voltage is applied across ends of conductor. The heat produced is

A constant voltage is applied across ends of conductor. The heat produced is:

- Directly proportional to length
- Inversely proportional to length
- Directly proportional to square of length
- None of these

Correct answer: 2. inversely proportional to length

## The 1 kHz signal has a period of 1 ms

The 1 kHz signal has a period of 1 ms

- FALSE
- TRUE

Correct answer: 2. TRUE

## The average value of a sine wave is 0.707 times the peak value

The average value of a sine wave is 0.707 times the peak value

- FALSE
- TRUE

Correct answer: 1. FALSE

## Periodic waveform is characterized by a repetition at fixed time intervals

Periodic waveform is characterized by a repetition at fixed time intervals

- FALSE
- TRUE

Correct answer: 2. TRUE

## The unit of frequency is the HERTZ

The unit of frequency is the HERTZ

- FALSE
- TRUE

Correct answer: 2. TRUE

## A signal having a 400 µs period has a frequency of

A signal having a 400 µs period has a frequency of

- 2,500 Hz
- 25,000 Hz
- 250 Hz
- 400 Hz

Correct answer: 1. 2,500 Hz

## Electric current flowing through the circuit produces

Electric current flowing through the circuit produces

- Chemical effect
- Luminous effect
- Magnetic effect
- Thermal effect

Correct answer: 4. Thermal effect

## The number of electrons in the outer most orbit of carbon atom is

The number of electrons in the outer most orbit of carbon atom is

- 3
- 4
- 6
- 7

Correct answer: 2. 4

## All good conductors possess high

All good conductors possess high

- Conductance
- Reluctance
- Resistance
- Thermal conductivity

Correct answer: 1. Conductance

## A glass rod when rubbed with silk cloth is charged since

A glass rod when rubbed with silk cloth is charged since

- It gives away electrons
- It gives away positive charge
- It takes in proton
- Its atoms are removed

Correct answer: 1. It gives away electrons

## When one leg of parallel circuit is opened out the total current will

When one leg of parallel circuit is opened out the total current will

- Become zero
- Decrease
- Increase
- Reduce

Correct answer: 2. Decrease

## Which of following can have negative temperature coefficient

Which of following can have negative temperature coefficient

- Compounds of silver
- Electrolytes
- Liquid metals
- Metallic alloys

Correct answer: 2. Electrolytes

## A 40 W bulb is connected in series with a room heater. If now 40 W bulb is replaced by 100 W bulb, the output of heater will

A 40 W bulb is connected in series with a room heater. If now 40 W bulb is replaced by 100 W bulb, the output of heater will

- Be zero
- Decrease
- Increase
- Remain same

Correct answer: 3. Increase

## The correct statement defining the semiconductor materials is

The correct statement defining the semiconductor materials is

- A semiconductor is a material made of alternate layers of conducting material and insulator
- A semiconductor is a material which has conductivity having average value of conductivity of metal and insulator
- A semiconductor is a material whose conductivity is same as between that of a conductor and an insulator
- A semiconductor is one which conducts only half of the applied voltage

Correct answer: 3. A semiconductor is a material whose conductivity is same as between that of a conductor and an insulator

## The property of a conductor because of which it passes current is known as

The property of a conductor because of which it passes current is known as

- Conductance
- Inductance
- Reluctance
- Resistance

Correct answer: 1. Conductance

## In case of direct current

In case of direct current

- Magnitude and direction of current changes with time
- Magnitude and direction of current remains constant
- Magnitude of current changes with time
- Magnitude of current remains constant

Correct answer: 2. Magnitude and direction of current remains constant

## The resistance of a conductor varies inversely with

The resistance of a conductor varies inversely with

- Area of cross-section
- Length
- Resistivity
- Temperature

Correct answer: 1. Area of cross-section

## Two bulbs of 500 W and 200 W rated at 250 V will have a resistance ratio as

Two bulbs of 500 W and 200 W rated at 250 V will have the resistance ratio as

- 2:5
- 25:4
- 4:25
- 5:2

Correct answer: 1. 2:5

## A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms respectively. The current in each branch is

A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms respectively. The current in each branch is

- 4.6 A, 6.9 A
- 4.6 A, 9.6 A
- 6.4 A, 6.9 A
- 6.4 A, 9.6 A

Correct answer: 4. 6.4 A, 9.6 A

## An electric filament bulb can be worked from

An electric filament bulb can be worked from

- AC supply only
- Battery supply only
- DC supply only
- All of above

Correct answer: 4. All of above

## The substances that have a large number of free electrons and offer a low resistance are known as

The substances that have a large number of free electrons and offer a low resistance are known as

- Conductors
- Inductors
- Insulators
- Semiconductors

Correct answer: 1. Conductors

## You have to replace 1500 ohms resistor in radio. You have no 1500 Ω resistor but have several 1000 Ω ones which you would connect

You have to replace 1500 ohms resistor in radio. You have no 1500 Ω resistor but have several 1000 Ω ones which you would connect

- Three in parallel
- Three in series
- Two in parallel
- Two in parallel and one in series

Correct answer: 4. Two in parallel and one in series

Solution: Req = (1000 || 1000) + 1000 = 500 + 1000 = 1500 ohms

## Voltage dependent resistors are generally made from

Voltage dependent resistors are generally made from

- Charcoal
- Graphite
- Nichrome
- Silicon carbide

Correct answer: 3. Nichrome

## The closed switch has a resistance of

The closed switch has a resistance of

- About 50 ohms
- About 500 ohms
- Infinity
- Zero

Correct answer: 4. Zero

## When electric current passes through a bucket full of water, lot of bubbling is observed. This suggests that the type of supply is

When electric current passes through a bucket full of water, lot of bubbling is observed. This suggests that the type of supply is

- AC
- DC
- Any of above
- None of these

Correct answer: 2. DC

## An open resistor, when checked with an ohmmeter reads

An open resistor, when checked with an ohmmeter reads

- High but within tolerance
- Infinite
- Low but not zero
- 0

Correct answer: 2. Infinite

## The conductance of an 8 ohm resistance is

The conductance of an 8 ohm resistance is

- 0.125 mS
- 12 S
- 125 mS
- 8 mS

Correct answer: 3. 125 mS

## The atomic number is defined as the number of neutrons in the nucleus

The atomic number is defined as the number of neutrons in the nucleus

- FALSE
- TRUE

Correct answer: 1. FALSE

## Materials that do not allow current under normal conditions is

Materials that do not allow current under normal conditions is

- Conductor
- Insulator
- Semiconductor
- Valence

Correct answer: 2. Insulator

## Electrons in the outer orbit are named

Electrons in the outer orbit are named

- Nuclei
- Shells
- Valences
- Waves

Correct answer: 3. Valences

## The current in a given circuit should not exceed 24 A. The recommended fuse should be

The current in a given circuit should not exceed 24 A. The recommended fuse should be

- 10
- 24 A
- A fuse is not essential
- 20

Correct answer: 2. 24 A

## A voltmeter is connected across the current path

A voltmeter is connected across the current path

- FALSE
- TRUE

Correct answer: 2. TRUE

## Which of the following is not an energy source

Which of the following is not an energy source

- Battery
- Generator
- Rheostat
- Solar cell

Correct answer: 3. Rheostat

## Materials with lots of free electrons are identified as

Materials with lots of free electrons are identified as

- Conductors
- Filters
- Insulators
- Semiconductors

Correct answer: 1. Conductors

## A wiper is the sliding contact in a

A wiper is the sliding contact in a

- Photoconductive cell
- Potentiometer
- Switch
- Thermistor

Correct answer: 2. Potentiometer

## An ammeter is connected across the current path

An ammeter is connected across the current path

- FALSE
- TRUE

Correct answer: 1. FALSE

## A crystal diode uses which characteristic for rectification

A crystal diode uses which characteristic for rectification

- Forward
- Forward or Reverse
- Reverse
- None of these

Correct answer: 1. Forward

## The designation rms means repetitions measured per second

The designation rms means repetitions measured per second

- FALSE
- TRUE

Correct answer: 1. FALSE

## A ramp is the type of waveform that is characterized by a non-linear increase or decrease in voltage or current.

A ramp is the type of waveform that is characterized by a non-linear increase or decrease in voltage or current.

- FALSE
- TRUE

Correct answer: 1. FALSE

## A phasor signifies

A phasor signifies

- The magnitude and a quantity direction
- The magnitude of a quantity
- The phase angle
- The width of a quantity

Correct answer: 1. The magnitude and a quantity direction

## A significant constraint of a crystal oscillator is

A significant constraint of a crystal oscillator is

- Its high output
- Its high Q
- Its low output
- Less availability of quartz crystal

Correct answer: 3. Its low output