NCERT Class VII: Science-Exercise Solutions

Chapter 14-Electric Current and its Effects-Exercise Solutions

NCERT Book Page Number-170
Q.1. Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery?
Answer:

Q.2. Draw the circuit diagram to represent the circuit shown in Fig?

 

Answer: In the above circuit one end of the bulb is connected to the battery and another end to the safety pin.
But the other end of the battery is not connected to the safety pin. Therefore there will be no flow of current as the switch is in “OFF” position.
This shows the circuit is not complete.
Circuit diagram of the above electric circuit will be:

Q.3. The given figure shows four cells fixed on a board.
Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

 

Answer:
In order to make battery, the positive terminal (+) of one cell should be connected to the (-) terminal of another cell and so on.

 

Q.4. The bulb in the circuit shown in figure does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

 

Answer: The positive terminal (+) of one cell should always be connected to negative terminal (-) of another cell.
But in case of above circuit both the positive terminals are connected to each other. This is the reason battery is not able to generate electricity.
Therefore the change which should be made to the circuit will be that the positive terminal (+) should be connected to negative terminal (-) of the cell and vice-versa.

 

NCERT Book Page Number-171
Q.5. Name any two effects of electric current.
Answer:
The two effects of electric current are:-
(i) Heating effect
(ii) Magnetic effect
Heating Effect of current: When an electric current passes through a wire, the wire gets heated. This is known as the heating effect of current.
The heating effect is used in many heating applications like electric heater, electric iron, light bulb etc.
Magnetic Effect of current: When an electric current flows through a wire, it generates magnetic field around it.
This effect is known as magnetic effect of current. Magnetic Effect of electric current has many applications like power lift, electric bell, electric fan etc.

 

Q.6. When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
Answer: The current flowing through the conducting wire creates magnetic field. When a compass is kept nearby this wire, it will experience two magnetic fields (one magnetic field due to wire and another magnetic field due to compass).
As a result when they interact with each other there will be deflection seen in the magnetic needle. When the current is switched off, there is no magnetic field produced by the wire, magnetic needle does not deflect from its north-south position.

 

Q.7. Will the compass needle show deflection when the switch in the circuit shown by Figure is closed?

 

Answer: There is no source of electric current i.e. (battery or cell). The circuit is an open circuit.
There will be no current flowing it, as a result, there will be no magnetic field produced by the wires.
Therefore there is no deflection shown by the compass needle.

Q.8. Fill in the blanks:
(a) Longer line in the symbol for a cell represents its _________terminal.
(b) The combination of two or more cells is called a _________.
(c) When current is switched ‘on’ in a room heater, it ________.
(d) The safety device based on the heating effect of electric current is called a ___________.
Answer: Longer line in the symbol for a cell represents its Positive.

 

• The combination of two or more cells is called a Battery.

 

Explanation: –
When a positive terminal of one cell is connected to a negative terminal of the second cell. Such a combination of two or more cells is called battery.
• When current is switched ‘on’ in a room heater, it ¬¬¬¬¬¬¬¬produces heat.
Explanation: –
When the electric current passes through the wire in the electric heater it becomes hot. This effect is known as heating effect of the electric current.

 

o The safety device based on the heating effect of electric current is called a fuse.
Explanation: –
A fuse is a safety device which limits current in circuit as a result it prevents damages to electrical circuits and possible fires.
Fuses used in electrical appliances.