Page 81 - Physics_Form_2
P. 81
Current electricity
some or all of the current flows from 4. Now disconnect the rheostat from
the designed path. Short-circuit faults the circuit and replace it with the
can be identified because the circuit or a two 2.5 V torch bulbs, also replace
section of the circuit draws an unusually the melted fuse with a new one as
high current (leading to fuse blowing). shown in Figure 2.46.
The potential difference between two
FOR ONLINE READING ONLY
points joined by a short circuit is zero or
much lower than expected. Activity 2.13
illustrate melting of fuse.
P Q
Activity 2.13
Aim: To demonstrate the melting Figure 2.46
of a fuse
5. Close the switch and observe the
Materials: two fuse wires 3 A, 3 size-D ammeter reading and the brightness
dry cells, rheostat, ammeter of the bulbs.
(0 – 5 A), two 2.5 V torch
bulbs with bulb holders, 6. Short-circuit the bulbs by connecting
connecting wires, switch, a lead wire across PQ with crocodile
crocodile clips clips. Observe the ammeter reading,
the brightness of the bulbs and the
Procedure fuse wire.
1. Connect the apparatus to make a Questions
circuit as shown in Figure 2.45. (a) Determine the current required to
E S
melt the fuse in Step 2.
(b) What was your observation on the
ammeter reading and the bulbs’
brightness when the switch was
closed in Step 3?
(c) What was the result of short-
circuiting in Step 6?
R h Fuse
Figure 2.45
When a current in the circuit exceeds
the current rating of a fuse wire, the fuse
2. Start with the rheostat set at wire melts. Putting a lead wire across
maximum resistance. PQ causes an increase in the ammeter
3. Close the switch and adjust the reading. It also causes bulbs to go off.
rheostat to raise the current. Observe These two observations are an indication
both the ammeter and the fuse wire. of a short circuit. The lead wire across PQ
Continue adjusting until the fuse is an unwanted connection which diverts
wire melts. Open the switch.
current through a different path. The lead
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Physics Form 2 Final.indd 75 25/10/2025 10:26
