Electricity Book Back Questions 8th Science Lesson 5

8th Science Lesson 5

5] Electricity

Book Back Questions with Answer and Do You Know Box Content

Do You Know?

A neutral object can become positively charged when electrons get transferred to another object; not by receiving extra positive charges.

If a positively charged glass rod is brought near another glass rod, the rods will move apart as they repel each other. If a positively charged glass rod is brought close to a negatively charged ebonite rod, the rods will move toward each other as they attract. The force of attraction or repulsion is greater when the charged objects are closer.

The materials which allow electric charges to pass through them easily are called conductors of electricity. For example, metals like aluminium, copper are good conductors of electricity. Materials which do not allow electric charges to pass through them easily are called insulators. Rubber, wood and plastic are insulators.

The first electroscope developed in 1600 by William Gilbert was called versorium. The versorium was simply a metal needle allowed to pivot freely on a pedestal. The metal would be attracted to charged bodies brought near.

Lightning’s extreme heat will vaporize the water inside a tree, creating steam that may burn out the tree.

During lightning and thunder, we should avoid standing in ground or open spaces. You should make yourself as small as possible by squatting. It is however safe to stay inside a car because the car acts as a shield and protects us from the electric field generated by the storm.

The electric eel is a species of fish which can give electric shocks of upto six hundred fifty watts of electricity. But if the eel repeatedly shocks, its electric organs become completely discharged. Then a person can touch it without being shocked.

Choose the best answers:

1. When an ebonite rod is rubbed with fur, the charge acquired by the fur is

(a) Negative

(b) Positive

(c) Partially positive and partly negative

(d) None of these

2. The electrification of two different bodies on rubbing is because of the transfer of

(a) Neutrons

(b) protons

(c) electrons

(d) Protons and neutrons

3. Which of the following a simple circuit must have?

(a) Energy source, Battery, Load

(b) Energy source, Wire, Load

(c) Energy source, Wire, Switch

(d) Battery, Wire, Switch

4. An electroscope has been charged by induction with the help of charged glass rod. The charged glass rod. The charge on the electroscope is

(a) Negative

(b) Positive

(c) Both positive and negative

(d) None of the above

5. Fuse is

(a) A switch

(b) A wire with low resistance

(c) A wire with high resistance

(d) A protective device for breaking an electric circuit

Fill in the blanks:

1. _________________ takes place by rubbing objects together.

2. The body which has lost electrons becomes ________________.

3. __________________ is a device that protects building from lightning strike.

4. ______________ has a thin metallic filament that melts and breaks the connection when the circuit is overheated.

5. Three bulbs are connected end to end from the battery. This connection is called _______________.

State true or false. If false, correct the statement:

1. The charge acquired by an ebonite rod rubbed with a piece of flannel is negative.

2. A charged body induces an opposite charge on an uncharged body when they are brought near.

3. Electroscope is a device used to charge a body by induction.

4. Water can conduct electricity.

5. In parallel circuit, current remains the same in all components.

Match the following:

1. Two similar charges – acquires a positive charge

2. Two dissimilar charges – prevents a circuit from overheating

3. When glass rod is rubbed with silk – repel each other

4. When ebonite rod is rubbed with fur – attract each other

5. Fuse – acquires a negative charge

Consider the statements given below and choose the correct option:

1. Assertion: People struck by lightning receive a severe.

Reason: Lightning carries very high voltage.

(a) Both assertion and reason are true and reason is the correct explanation of the assertion.

(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) Assertion is true, but reason is false.

(d) Both assertion and reason are false.

2. Assertion: It is safer to stand under a tall tree during lightning.

Reason: It will make you the target for lightning.

(a) Both assertion and reason are true and reason is the correct explanation of the assertion.

(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) Assertion is true, but reason is false.

(d) Both assertion and reason are false.

Answers:

Choose the best answers:

1. Positive 2. Electrons 3. Battery, Wire, Switch 4. Positive 5. a protective device for breaking an electric circuit

Fill in the blanks:

1. Transfer of electrons 2. Positive 3. Lightning arrestor 4. Electric fuse 5. Series circuit

State true or false. If false, correct the statement:

1.True

2.True

3.True

4.True

5.False

Correct answer: In parallel circuit, current remains the same in all components.

Match the following:

1.Two similar charges- repel each other

2.Two dissimilar charges- attract each other

3.When glass rod is rubbed with silk- acquires a positive charge

4.When ebonite rod is rubbed with fur- acquires a negative charge

5.Fuse- prevents a circuit from overheating

Consider the statements given below and choose the correct option:

1.Both assertion and reason are true and reason is the correct explanation of assertion

2.Assertion is false but reason is true