LIVING SCIENCE

ELECTRIC CURRENT AND ITS EFFECTS

CHOOSE THE MOST APPROPRIATE ANSWER

Question 1:

Which of these is not a circuit element?

(a) potential difference

(b) voltmeter
(c) resistor
(d) battery
ANSWER:

(a) potential difference

It is the difference between the potentials of two terminals of a battery or any other current
source connected to a circuit.

Question 2:

The necessary requirement for a fuse wire is

(a) conductor with low melting point

(b) conductor with high melting point
(c) insulator with low melting point
(d) insulator with high melting point
ANSWER:

(a) conductor with low melting point

A fuse is a safety device made up of a conducting material having low melting point. It
works on the principle of heating effect of current.

Question 3:

The strength of a magnetic field due to a solenoid can be increased by

(a) increasing the number of turns in the solenoid

(b) increasing the current in the solenoid
(c) winding the solenoid around a magnetic material
(d) all of these
ANSWER:

(d) all of these

The strength of a magnetic field due to a solenoid can be increased by increasing the
number of turns in the solenoid. It can also be increased by increasing the current and
winding the solenoid around a magnetic material.

Question 4:

Which of these appliances does not use an electromagnet?

(a) washing machine

(b) refrigerator
(c) room heater
(d) electric bell
ANSWER:

(c) room heater

A room heater does not use an electromagnet. The heating effect of current is used in an
electric heater.

Question 5:

Which of these is absolutely necessary in an electric circuit?

(a) bulb
(b) switch
(c) voltmeter
(d) connecting wires
ANSWER:

(d) connecting wires

All the given options play an important role in an electric circuit but connecting wires are
absolutely necessary to complete the circuit.
Question 6:

The same current is passed through the following. Which will show the strongest magnetic
strength?

(a) straight conducting wire

(b) coil of wire
(c) solenoid wound on a wooden core
(d) solenoid wound on an iron core
ANSWER:

(d) solenoid wound on an iron core

It will show the strongest magnetic strength. It is strong enough to attract metal paper clips
as well as big iron nails.

B. VERY SHORT ANSWER QUESTION:

Question 1:

Which insulator does a switch use to cut off the current in a circuit?
ANSWER:

Air is used as an insulator in a switch to cut off the current in a circuit.

Question 2:

Metals are conductors of electricity. True or false?

ANSWER:

True.
Metals are conductors of electricity. The free and mobile electrons present in the metals are
responsible for their high thermal and electrical conductivity.

Question 3:

Every conductor offers resistance to the flow of electric current. True of false?
ANSWER:

True; all conductors offer some resistance to the flow of electric current. While some metals
like copper offer very little resistance, others such as tungsten offer high resistance.

Question 4:

We use symbols to draw a circuit __________

ANSWER:

We use symbols to draw a circuit element.

Question 5:

A point A in a circuit is at a lower potential than point B. In which direction will the current
flow in the circuit?
ANSWER:

In an electric circuit, electrons flow from low to high potential. In contrary, current flows from
high to low potential.
Thus, current will flow from B to A in the given circuit.

Question 6:

In circuit, a conductor offering low resistacne will heat up more than conductor offering high
resistance. True of false?
ANSWER:

False; a conductor offering low resistance will heat up less than the conductor offering high
resistance.
The greater the resistance offered by the conductor to the flow of current, the greater would
be the heat generated.

Question 7:
Which effect of current does the filament in eletric bulb utilize?
ANSWER:

Heating effect of current is used in the filament of an electric bulb.

Question 8:

The core of an electromagnet can be made up of any metal. True of false?

ANSWER:

False; the core of an electromagnet must be a metal that can allow current to flow and can
produce necessary magnetic field.

Question 9:

An ____________ behaves like a magnet when an electric current passes through it.
ANSWER:

An electromagnet behaves like a magnet when an electric current passes through it.

Question 10:

An electric bell has an arrangement to supply intermittent current to the electromagnet in it.
True or False?
ANSWER:

True; an electric bell has an arrangement to supply intermittent current to the electromagnet
in it.

C. SHORT ANSWER QUESTIONS

QUESTION1
What is an electric circuit?
ANSWER:

An electric circuit can be defined as a closed path through which electric current can flow.
Various components such as battery, resistor, wire, key, bulb etc. can be connected in
different ways to construct an electric circuit.

Question 2:

What is the relationship between potential difference and direction of flow of current in an
electric circuit?
ANSWER:

Potential difference is the difference in the potential between two terminals of a battery or
any other current source connected to an electric circuit. In the circuit, current flows from
high to low potential because electrons flow from low potential to high potential.

Question 3:

Does every conductor heat up when an electric current is passed through it? What does the
amount of heat depend on? Name the conductor normally used in heating appliances.
ANSWER:

Yes, every conductor heats up when electric current is passed through it. Heating is caused
by the resistance provided by the conductor to the current flowing through it. The amount of
heat depends on the length, thickness and nature of the material of conductor.

Nichrome is used in heating appliances as it offers high resistance to the flow of current.

Question 4:

A domestic circuit develops a short circuit. What will be the effect on a fuse wire connected
in the circuit?
ANSWER:
A fuse wire is made up of an alloy with a low melting point. The heat produced due to short
circuit melts the fuse wire and breaks the circuit.

Question 5:

What is a miniature circuit breaker?

ANSWER:

Miniature circuit breaker is a switch that automatically stops the current in a circuit if the
current in it exceeds the specified maximum limit.
Question 6:

Draw the symbols used in a circuit for-a battery of four cells, a switch, a lamp.
ANSWER:

A battery of four cells:

Switch in the ‘ON’ position:

Switch in the ‘OFF’ position:

Lamp:

D. LONG ANSWER QUESTIONS

Question 1:

Draw a circuit diagram of a dry cell connected to a bulb through a switch. Mark the positive
and negative terminals of the cell, and the direction of flow of current in the diagram.
ANSWER:
Question 2:

How can you increase the magnetic strength of a solenoid?

ANSWER:

Magnetic strength of a solenoid can be increased by:

(i) Increasing the number of turns in the solenoid

(ii) Increasing the current in the solenoid
(iii) Winding the solenoid around a magnetic material

Question 3:

What is an electromagnet? Give three uses of electromagnets.

ANSWER:

An electromagnet is a coil of insulated wire wound around a piece of a magnetic substance

such as soft iron. The magnetic substance acts as a magnet as long as the current flows in
the wire.

Uses of electromagnet:

(i) Electromagnets are used in a number of electric appliances such as electric bells and
electric buzzers.
(ii) They are used in electric motors, which find wide application in fans, washing machines
etc.
(iii) Very strong electromagnets are used in factories and cranes for lifting heavy iron
pieces.
Question 4:

Explain the working of a simple electric bell.

ANSWER:

An electric bell works with the help of an electromagnet. It is made up of a coil of wire
wound on an iron piece, which acts as an electromagnet. On passing the current, magnetic
field is produced by the electromagnet.

The hammer of the bell is attracted towards the electromagnet when the circuit is complete.
Further, the circuit breaks after the hammer moves towards the electromagnet. When the
circuit breaks, the electromagnet doesn’t attract the hammer. The hammer comes back to
its original position due to spring effect. As the hammer comes back to its original position, it
touches the metal connector and the circuit is complete again. This cycle continues till the
key is kept ON.

HOTS QUESTIONS

Question 1:

Fuse wires of miniature circuit breakers are not used in a circuit containing electric cells.
Why?
ANSWER:

MCBs are most commonly used in place of fuses because it is easier to turn on an MCB
when it gets tripped.
In a circuit where electric cells are used to supply low values of voltage and current, no
fuses are required because there is very little risk of short circuit. To avoid any accident,
these fuses are used in circuits where high voltages and currents are delivered.

Question 2:

Can you use a copper wire to make the filament of an electric bulb? Why?
ANSWER:

Filament of an electric bulb is made up of conductors that offer high resistance to electric
current. Copper wire cannot be used in filaments because it offers very little
resistance. ​Tungsten is used for making the filaments as it offers high resistance.
Question 3:

Mohit used a fuse wire with a specification of 5 amperes in a circuit connected to an air
conditioner which draws a current of 10 amperes. What will happen when the air conditioner
is switched on? What will you advise him to do?
ANSWER:

When the air conditioner is switched on, the fuse wire will melt due to extra current.

The fuse wire must be selected keeping in mind the minimum current that will melt it. Its
specification should be slightly more than the normal operating current of the electrical
appliance.

Mohit should be advised to use a fuse wire with a specification of 15 amperes.

Question 4:

Rita used a fuse wire with a 100 amperes specification in a circuit at home which draws a
maximum current of 20 amperes when all devices in the circuit are switched on. Do you
think she used the correct fuse wire? What will you advise her to do?
ANSWER:

No, Rita did not use the correct fuse wire. The ampere rating of a fuse should not exceed
the current carrying capacity of the circuit except in some cases.
In the given circuit, she should use a fuse wire with 20 amperes specification.

Question 5:

You have seen that the heating effect of current can be put to good use. Can you think of
situations where this effect results in wastage of energy?
ANSWER:

Yes, when electric current passes through long conductors, a portion of energy is wasted in
the form of heat. Also, in case of an incandescent lamp, only a part of electricity is
converted into light and the rest is wasted as heat, which is unwanted.
Question 6:

A coil with no current passing through it is suspended freely. It points in the east-west
direction. Explain what will happen if a current is passed thourgh the coil.
ANSWER:

Current flowing through a wire gives rise to a magnetic field around it. Therefore, if current
is passed though the coil, it will become a magnet and will align along the north-south
direction.