Page 18 - Physics_Form_2

Physics for Secondary Schools

Procedure When the plastic comb is rubbed with
1. Suspend an iron nail from a string, cotton, it becomes negatively charged.
as shown in Figure 1.14. When the comb is placed near the iron

2. Rub the comb with a piece of cotton nail, the conduction electrons at the end
cloth. of the iron nail near the negative charge
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3. Bring the comb near one end of the on the comb are repelled and move to the
iron nail. opposite end of the iron nail. This leaves

4. Rub the glass rod with a piece of an excess positive charge at the end near
woollen cloth. the comb. The positive charges on the iron
5. Bring the glass rod near one end of nail then attract the negative charges from
the iron nail. the comb. Further observation reveals that
the iron nail is slightly pulled towards the
Woollen cloth comb, as shown in Figure 1.15.

Conduction
Glass rod Iron nail electrons
repelled

Comb

Figure 1.15: Charging a conductor
by induction using a
Cotton cloth negatively charged comb

On the other hand, rubbing the glass rod
with cotton causes it to acquire a positive
Figure 1.14
charge. When the rod is brought close
Questions to an iron nail, the conduction electrons
(a) What do you observe in steps 3 and from the iron nail are attracted by the
5? positive charge of the rod and move to
(b) What type of charge does the comb the end of the iron nail near the glass
acquire? rod. This movement results in an excess

(c) Explain your results. of positive charge at the opposite end of
the iron nail. As a result, the iron nail is
(d) Why does a string suspend the iron pulled slightly towards the glass rod, as
nail? shown in Figure 1.16.

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Student’s Book Form Two

Physics Form 2 Final.indd 12 25/10/2025 10:25