Electricity Test

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Electricity Test - 25

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Weekly Quiz Competition

Question 1
1 / -0

A man has five resistors each of value $$\frac {1}{5}\Omega $$. What is the maximum resistance he can obtain by connecting them?

A
$${1} \Omega $$

B
$$5 \Omega $$

C
$$\dfrac {1}{2} \Omega $$

D
$$\dfrac {2}{5} \Omega $$

Solution

Maximum resistance is obtained when all the resistors are connected in series.
Effective resistance $$R_{max} = R+R+R+R+R = 5R$$
$$\therefore$$ $$R_{max} = 5\times \dfrac{1}{5} =1\Omega$$
Question 2
1 / -0

When a current flows through a conductor, its temperature

A
increases

B
decreases

C
remains same

D
may increase or decrease

Solution

As we know,
$$Power=I^2R$$
Therefore, this power is released in the form of heat in the conductor and this heat increases the temperature of the conductor.
Hence, temperature increases.
Question 3
1 / -0

The maximum number of 40 W bulbs connected in parallel which can be lighted safely using a 240 V supply with a 5A fuse is.

A
30

B
45

C
8

D
44

Solution

Answer is A.

Fuses are safety devices that are to be built into our electrical system. If there were no fuses and we operated too many appliances on a single circuit, the cable carrying the power for that circuit would get extremely hot, short circuit, and possibly start a fire. To prevent electrical overloads, fuses are designed to trip or blow, stopping the flow of current to the overloaded cable.
The fuse must always be connected to the mains and it must be of correct value. For example, a 15-ampere fuse should trip when the current through it exceeds 15 amperes. A 20-ampere fuse should blow when the current through it exceeds 20 amps.
In this case, the bulb is 40 W and the voltage is 240 V.
That is, P = VI, I = P/V = 40/240 = 0.16 A.
The current drawn from a single 40 W bulb is 0.16 A.
Therefore, with a fuse of 5 A, let the number of bulbs that can be used is given as follows.
I * x = 5 A, That is, x = 5/0.16 = 31.
So, 30 bulbs can burn with a 5 A fuse.
Question 4
1 / -0

Which among the following is the commercial unit of electrical energy?

A
Volt

B
Watt

C
Ampere

D
KWh

Solution

Answer is D.

The kilowatt-hour is a unit of energy equal to 1,000 watt-hours, or 3.6 mega-joules. If the energy is being transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatt-hours is the product of the power in kilowatts and the time in hours. The kilowatt-hour is commonly used as a billing unit for energy delivered to consumers by electric utilities.
Question 5
1 / -0

If the current passing through an electric bell is doubled, the heat produced will become

A
four times

B
double

C
one-fourth

D
half

Solution

Answer is A.

Energy ($$power\times time$$) is measured in Joules and by including time (t) in the power formulae, the energy dissipated by a component or circuit can be calculated.
Energy dissipated = Pt or $$VI\quad \times \quad t\quad as\quad P=VI$$.
It can also be written as $${ I }^{ 2 }\times Rt\quad as\quad V=IR.$$
Hence, the expression for Power in terms of current is given as $$P={ I }^{ 2 }Rt\quad J$$.
Therefore, if I becomes 2I, then $$P'=(2{ I) }^{ 2 }R\times t\quad =\quad 4({ I }^{ 2 }R\times t)$$.
Hence, if the current passing through an electric bell is doubled, the heat produced will become four times more.
Question 6
1 / -0

Which is represented by the electric current?

A
Charge per unit volume

B
Charge per unit time

C
Charge per unit area

D
Both A .and B

Solution

An electric current is a flow of electric charge. In electric circuits, this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in a plasma.
It is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes. It is the charge per unit time.
Option B.
Question 7
1 / -0

A material that does not allow electricity to flow through it is called a/an-

A
Electrical appliance

B
Electrical conductor

C
Electrical Insulator

D
None of these

Solution

An electrical insulator is a material whose internalelectric charges do not flow freely; very little electriccurrent will flow through it under the influence of anelectric field. This contrasts with other materials, semiconductors and conductors, which conductelectric current more easily.
Question 8
1 / -0

The amount of heat produced in a wire depends on its material-

A
Length

B
Thickness

C
Length and thickness

D
None of these

Solution

Amount of heat produced in wire = $$I^2R$$
Where $$R$$ = Resistance of wire
$$I$$ = Current through wire
As resistance of wire $$R \propto \dfrac{L}{A}$$
So heat produced depends on Length as well as thickness.
Question 9
1 / -0

Electric current can flow through-

A
Silver

B
Copper

C
Iron

D
All of these

Solution
Question 10
1 / -0

Most of the electricity carrying wires near highways do not have a plastic covering like the wires used at homes. But there is no substantial loss of energy because

A
Air is a bad insulator of electricity

B
Air is a bad conductor of electricity

C
Electricity flows very fast near highways

D
Both B & C

Solution

Most of the electricity carrying wires near highways do not have a plastic covering like the wires used at homes because air is a bad conductor of electricity. Hence there is no substantial loss of energy during the flow of electricity in the overhead electric wires on the road and at homes, the plastic covering is used as insulator.

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Electricity Test - 25

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Electricity Test - 25

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Question 1

$${1} \Omega $$

$$5 \Omega $$

$$\dfrac {1}{2} \Omega $$

$$\dfrac {2}{5} \Omega $$

Solution

Question 2

increases

decreases

remains same

may increase or decrease

Solution

Question 3

30

45

8

44

Solution

Question 4

Volt

Watt

Ampere

KWh

Solution

Question 5

four times

double

one-fourth

half

Solution

Question 6

Charge per unit volume

Charge per unit time

Charge per unit area

Both A .and B

Solution

Question 7

Electrical appliance

Electrical conductor

Electrical Insulator

None of these

Solution

Question 8

Length

Thickness

Length and thickness

None of these

Solution

Question 9

Silver

Copper

Iron

All of these

Solution

Question 10

Air is a bad insulator of electricity

Air is a bad conductor of electricity

Electricity flows very fast near highways

Both B & C

Solution

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