Page 126 - Physics Form 5 KSSM_Neat

Based on Activity 3.6, a comparison between electromotive force and potential difference is
shown in Table 3.12.
Table 3.12 Comparison between electromotive force and potential difference
Electromotive force (e.m.f.), Ԑ Potential difference, V

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V
V

No current flows in the circuit A current flows in the circuit

The voltmeter reading in an open circuit is the The voltmeter reading in a closed circuit is the
electromotive force, Ԑ. potential difference across the bulb, V.

Work done by an electrical source to move one Work done to move one coulomb of charge
coulomb of charge in a complete circuit. between two points.

Internal Resistance
Based on Activity 3.6, the value of potential difference across the bulb, V is smaller than the
e.m.f., Ԑ of the dry cell. This indicates that there is a voltage drop. What causes the voltage drop
in the dry cell?

Activity 3.7

Aim: To study the effect of internal resistance on voltage drop
Apparatus: Two 1.5 V dry cells from two different brands (brands A and B), cell holder, switch,
bulb with holder, connecting wires, ammeter and voltmeter
Instructions:
1. Check the dry cells you are using. Make sure both dry cells are new.
2. Set up the apparatus as shown in Figure 3.24 using the brand A dry cell.
V

A Switch

Bulb
Figure 3.24
116 LS 3.3.1 3.3.2