Question1.

Fill in the blanks in the following

• A device that is used to break an electric circuit is called _______.
• An electric cell has _____ terminals.

Answer:

(a) A device that is used to break an electric circuit is called electric switch.

Explanation:-

A switch is a simple device that either breaks the circuit or completes it.

Switch is 'OFF'

When switch is in ‘OFF’ position, then the circuit is open i.e. no current flows through the circuit and when switch is in ‘ON’ position, then the circuit is complete i.e. current flows through the circuit.

Switch is 'ON'

(b) An electric cell has two terminals.

Explanation:-

An electric cell has 2 terminals positive and negative.

Electrical Cell

Question2.

Mark 'True' or 'False' for following statements:

(a) Electric current can flow through metals.

(b) Instead of metal wires, a jute string can be used to make a circuit.

(c) Electric current can pass through a sheet of thermoCol.

Answer:

(a) Electric current can flow through metals. (True)

Explanation: -

As metals are good conductors of electricity so they allow current to flow them easily.

(b) Instead of metal wires, a jute string can be used to make a circuit. (False)

Explanation: -

As Jute is bad conductor of electricity therefore if jute string is used to make an electric circuit, then the current will not flow through it.

(c) Electric current can pass through a sheet of thermo Col. (False)

 Explanation: -

ThermoCol is a bad conductor of electricity.

Question 3.

Explain why the bulb would not glow in the arrangement shown in Fig (1).

Answer:

In the given figure, it can be seen that one terminal of the bulb is connected to screw driver. The handle of screw driver is made up of insulator, which is bad conductor of electricity. It won’t allow electric current to pass through. Therefore in the above circuit the bulb will not glow.

Question 4.

Complete the drawing shown in Fig (2) to indicate where the free ends of the two wires should be joined to make the bulb glow.

Answer:

The given circuit is not complete as one of the ends of the cell is not connected to the switch and the bulb .As a result no current flows through the circuit. In order to complete the circuit the positive terminal of the cell should be connected to the one end of the switch and then to the bulb. Then the bulb will start glowing. Therefore the circuit will be as shown in the figure below:-

Question 5.

What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.

Answer:

A switch is a simple device that either breaks the circuit or completes it. If the switch is “ON” then the current flows through the circuit and when the switch is “OFF” then the current cannot flow through the circuit. Electrical appliances such as table fans, electric lamps, washing machines, juicers and mixers, radio, TV, mobiles, torch and electric toys have in built switches.

Question 6.

Would the bulb glow after completing the circuit shown in Fig (3), if instead of safety pin we use an eraser?

Answer:

Erasers are bad conductors of electricity. They do not conduct electricity. The circuit becomes an open circuit. Therefore the bulb won’t glow if safety pin is replaced with an eraser.

Question 7.

Would the bulb glow in the circuit shown in Fig. (5)?

Answer:

The bulb will not glow, because both the terminals are connected to the single terminal of the bulb. The following correction should be made in order for the bulb to glow:-

Question 8.

Using the "conduction tester" on an object it was found that the bulb begins to glow. Is that object a conductor or an insulator? Explain.

Conduction Circuit

Answer:

Current flows through objects which are good conductors of electricity. When the two ends of a conduction tester are touched with an object, then the bulb will start glowing. This shows that the object is a conductor. This type of circuit is known as conduction tester circuit.

Question 9.

Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.

Answer:

Human body is good conductor of electricity so if electrician touches any live wire with his hands he will get an electric shock. So in order to avoid the shock they wear rubber gloves because rubber is a poor conductor of electricity. So rubber will protect electrician from electric shock.

Gloves

Question 10.

The handles of the tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them. Can you explain why?

Answer:

Rubber or Plastics are insulators i.e. they don’t allow current to pass through them. Therefore the handles of the tools like screwdrivers and pliers etc. which are used by electricians for repair work usually have plastic or rubber covers on them. This protects them against any electric shock.