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A heater coil is cut into two equal parts and only one part is now used in the heater. The heat generated will now be

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Important Questions on Current Electricity

EASY

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

In which of the following devices, the eddy current effect is not used?

HARD

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A light bulb of resistance $R = 16 Ω$ is attached in series with an infinite resistor network with identical resistances as shown below. A $10 V$ battery derives a current in the circuit. What should be the value of $r$ such that the bulb dissipates about $1 W$ of power?

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HARD

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

The resistance of an electrical toaster has a temperature dependence given by

R (T) = R_{0} [1 + α (T - T_{0})]

in its range of operation. At

T_{0} = 300 K, R = 100 Ω and a t T = 500 K, R = 120 Ω

. The toaster is connected to a voltage source at

200 V

and its temperature is raised at a constant rate from

300 to 500 K

30 s

. The total work done in raising the temperature is :

Note: This question was awarded as the bonus since all options were incorrect in the exam.

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

In a building there are

15

bulbs of

45 W

15

bulbs of

100 W, 15

small fans of

10 W

and

2

heaters of

1 k W

. The voltage of electric main supply is

220 V

. The minimum fuse capacity (rated value) of the building will be:

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

Two electric bulbs, rated at

(25 W, 220 V)

and

(100 W, 220 V),

are connected in series across a

220 V

voltage source. If the

25 W

and

100 W

bulbs draw powers

P_{1}

and

P_{2}

respectively, then:

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Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A cell of internal resistance

r

drives current through an external resistance

R .

The power delivered by the cell to the external resistance will be maximum when:

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Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A uniform metallic wire of length $L$ is mounted in two configurations. In configuration $1$ (triangle), it is an equilateral triangle and a voltage, $V$ is applied to corners $A$ and $B$ . In configuration $2$ (circle), it is bent in the form of a circle, and the potential $V$ is applied at diametrically opposite points $P$ and $Q$ . The ratio of the power dissipated is configuration $1$ to configuration $2$ is.

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EASY

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A resistor develops

500 J

of thermal energy in

20 s

when a current of

1.5 A

is passed through it. If the current is increased from

1.5 A

3 A

, what will be the energy developed in

20 s

HARD

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

The supply voltage to a room is

120 V

. The resistance of the lead wires is

6 Ω

. A

60 W

bulb is already switched on. What is the decrease of voltage across the bulb, when a

240 W

heater is switched on in parallel to the bulb?

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A filament bulb

(500 W, 100 V)

is to be used in a

230 V

main supply. When a resistance,

R

is connected in series, it works perfectly and the bulb consumes

500 W

. The value of

R

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Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

Consider the following two circuits

$[A] :$ $20$ bulbs are connected in series to a power supply line

$[B] :$ $20$ bulbs identical to $[A]$ are connected in a parallel circuit to an identical power supply line

Identify which of the following is not true

EASY

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

The charge flowing through a resistance

R

varies with time

t

Q = a t - b t^{2}

where

a

and

b

are positive constants. The total heat produced in

R

is:

HARD

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A student in a town in India, where the price per unit (1 unit

= 1 kWh

) of electricity is

₹ 5.00,

purchases a

1 kVA

UPS (uninterrupted power supply) battery. A day before the exam, 10 friends arrive to the student's home with their laptops and all connect their laptops to the UPS. Assume that each laptop has a constant power requirement of

90 W

. Consider the following statements.
I. All the 10 laptops can be powered by the UPS, if connected directly.
II. All the 10 laptops can be powered, if connected using an extension box with a 3 A fuse.
III. If all the 10 friends use the laptop for

5 h

, then the cost of the consumed electricity is about

₹ 22.50 .

Select the correct option with the true statements.

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Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

The resistive network shown below is connected to a

D . C .

source of

16 V .

The power consumed by the network is

4 W

. The value of

R

is:

EASY

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

Two electric bulbs rated

P_{1}

watt,

V

volts and

P_{2}

watt,

V

volts are connected in parallel and

V

volts are applied to it. The total power will be :-

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Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A small town is located

10 km

away from a power plant. An average of

120 kW

of electric power is sent to this town. The transmission lines have a total resistance of

0.40 Ω .

Calculate the power loss, if the power is transmitted at

240 V .

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Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

The resistor

R_{1} = 3 Ω

and

R_{2} = 1 Ω

are connected in parallel to a

20 V

battery. Find the heat developed in the resistor

R_{1}

in one minute

EASY

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

If the current through a resistor in a circuit increases by

3 %,

the power dissipated by the resistor

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Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

A current of

2 mA

was passed through an unknown resistor which dissipated a power of

4.4 W .

Dissipated power when an ideal power supply of

11 V

is connected across it is:

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Energy and Electrical Power

The power dissipated in the circuit shown in the figure is

30 W

. The value of

R

A heater coil is cut into two equal parts and only one part is now used in the heater. The heat generated will now be

Important Questions on Current Electricity

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