Q

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

P Pankaj Sanodiya

A switch is an electric device that is used to complete or break an electric circuit. If the switch is 'ON', then current can flow through the circuit. However, if the switch is 'OFF', then the current cannot flow through the circuit.

We use an electric switch to get control over the electrical appliances and use them only when needed.

Electrical appliances such as table fans, electric lamps, washing machines, juicers and mixers, TV, radio, etc. have switches built into them.

4. Complete the drawing shown in Fig 12.14 to indicate where the free ends of the two wires should be joined to make the bulb glow.

P Pankaj Sanodiya

in order to light the bulb, we have to complete the circuit as current flows in closed loops.

Hence we add one end of the wire to the terminal of the battery and another end of the wire to the bulb. this will complete the circuit and the bulb will glow.

3. Explain why the bulb would not glow in the arrangement shown in Fig. 12.13.

P Pankaj Sanodiya

The bulb will not glow as there is an insulator( the plastic-coated part ) connected in the circuit. the current will not pass through it will not make a complete circuit for the current to flow.

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

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

P Pankaj Sanodiya

False, Sheet of thermocol is an insulator and current don't pass through insulators.

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

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

P Pankaj Sanodiya

No, the metal wire can not be replaced with jute strings in order to conduct electricity in the circuit. metal wires are the conductor of electricity while jute strings are not.

2. Mark 'True' or 'False' for following statements: (a) Electric current can flow through metals.

P Pankaj Sanodiya

True. Metals have free electron in their atoms that's why they can conduct electricity because electric current is nothing but the flow of electrons.

1. Fill in the blanks :

(b) An electric cell has _______________ terminals.

P Pankaj Sanodiya

An electric shell has two terminal.One positive and one negative.

1. Fill in the blanks : (a) A device that is used to break an electric circuit is called _______________.

P Pankaj Sanodiya

A device that is used to break an electric circuit is called a Fuse.

10. Give two examples of periodic motion.

D Divya Prakash Singh

Two examples of periodic motion are:

(i) The needle of a sewing machine.

(ii) The blades of a fan which is switched on.

9. Why would you not like to use a measuring tape made of an elastic material like rubber to measure distance? What would be some of the problems you would meet in telling someone about a distance you measured with such a tape?

D Divya Prakash Singh

A measuring tape made of elastic material would be stretchable and while measuring the distance between two points it might get stretched and would give incorrect measurement.

8. Write the similarities and differences between the motion of a bicycle and a ceiling fan that has been switched on.

D Divya Prakash Singh

Similarities between the motion of a bicycle and a ceiling fan that has been switched on are:

(i) The blades of the fan and the wheels of the bicycle are in circular motion.

(ii) The blades of the fan and spokes of the wheels of the bicycle are fixed at a certain point.

Differences between the motion of a bicycle and a ceiling fan that has been switched on are:

(i) The bicycle is in linear motion unlike the fan.

(ii) The motion of the blades of the fan is periodic whereas that of the cycle is rectilinear.

7. While measuring the length of a knitting needle, the reading of the scale at one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?

D Divya Prakash Singh

Reading of the scale at one end = 3.0 cm.

Reading of the scale at the other end = 33.1 cm.

Length of the scale = 33.1 cm - 3.0 cm = 30.1 cm

6. The distance between Radha's home and her school is 3250 m. Express this distance into km.

D Divya Prakash Singh

$\\1\ km = 1000\ m \\1\ m = \frac{1}{1000}\ km = 0.001\ km \\3250\ m\ =3250\times 0.001\ km = 3.25\ km$

The distance between Radha's home and her school is 3.25 km

5. The height of a person is 1.65 m. Express it into cm and mm.

D Divya Prakash Singh

$\\1\ m = 100\ cm \\1.65\ m = 1.65\times 100\ cm = 165\ cm \\1\ cm = 10\ mm \\165\ cm = 165\times 10\ mm = 1650\ mm$

The height of the person in centimetres is 165 cm and in millimetre is 1650 mm.

4. Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre,1 millimetre.

$\\1\ cm = 10 \ mm. \\1\ m = 100\ cm = 100\times 10\ m=1000\ mm \\1\ km = 1000\ m = 1000\times 1000\ mm= 1000000\ mm$