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#### Question 1:

What is an electric circuit?

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 1:

Which of these is not a circuit element?

(a) potential difference
(b) voltmeter
(c) resistor
(d) battery

(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

(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

(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

(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

(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

(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.

#### Question 1:

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

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?

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?

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 __________

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?

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?

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?

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?

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.

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?

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

#### Question 2:

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

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.

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?

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?

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.

A battery of four cells:

Switch in the ‘ON’ position:

Switch in the ‘OFF’ position:

Lamp:

#### 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.

#### Question 2:

How can you increase the magnetic strength of a solenoid?

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.

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.

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.

#### Question 1:

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

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?

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?

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?

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?

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.