Class 7 Electricity and Its Effect

When an electric current flows through a copper wire AB as shown in Figure14.1, the wire

• deflects a magnetic needle placed near it

• becomes red hot

• gives electric shock

• behaves like a fuse

Choose the statement which is not correct in the case of an electric fuse.

• Fuses are inserted in electric circuits of all buildings

• There is a maximum limit on the current which can safely flow through the electric circuits

• There is a minimum limit on the current which can safely flow in the electric circuits

• If a proper fuse is inserted in a circuit it will blow off if current exceeds the safe limit.

Three bulbs A, B, C are connected in a circuit as shown in Figure 14.2. When the switch is ‘ON’

• bulb C will glow first

• bulb B and C will glow simultaneously and bulb A will glow after some time

• all the bulbs A,B and C will glow at the same time

• the bulbs will glow in the order A, B and C

When a switch is in OFF position, When a switch is in OFF position (i) circuit starting from the positive terminal of the cell stops at the switch. (ii) circuit is open. (iii) no current flows through it. (iv) current flows after some time. Choose the combination of correct answer from the following.

• all are correct

• (ii) and (iii) are correct

• only (iv) is correct

• only (i) and (ii) are correct

Which of the following precautions need not be taken while using electric gadgets/appliances/circuit?

• We should never touch a lighted electric bulb connected to the mains

• We should never experiment with the electric supply from the mains or a generator or an inverter

• We should never use just any wire or strip of metal in place of a fuse

• We should never turn the switch in ON position.

Which property of a conducting wire is utilised in making electric fuse?

• High boiling point

• Low boiling point

• High melting point

• Low melting point

Name the device used these days in place of electric fuses in electrical circuits.

• Miniature Circuit Breaker

• voltage regulator
• power strip
• fuse box

Fill in the blanks: Our body is a ________________ of electricity.

• magnet
• conductor
• generator
• insulator

Fill in the blanks: An electric cell produces electricity from the __________
___________ in it.

• metals
• water
• light
• chemicals

Fill in the blanks: In an electric circuit a fuse is a ________________ to
prevent possible fire.

• fire extinguisher
• light bulb
• safety device
• screwdriver