Evergreen Secondary School
Name: ………………………………………. (
Class: …………………………………………
Secondary Two Science(Physics)
)
Date: ………………………………….
CURRENT ELECTRICITY WORKSHEET 02 – emf, potential difference
A
Concept of Electromotive Force and Potential Difference
1.
Define electromotive force (e.m.f.)
[1]
E.m.f is the amount of energy used to drive a unit charge around a complete circuit.
2.
When there is battery connected to a circuit, charges flow around the circuit. Explain why there is a
flow of charge around the circuit.
[1]
Battery is the source of energy, which energise the charges when they passes through it, hence
the charge flow around the circuit in a particular direction.
3.
Consider a torch light without battery and a circuit using a cell to light up a lamp. Both set up light
can up the lamps.
Setup A: A torch light which does not need to use batteries.
Setup B: Lamps use a battery.
Explain why both set ups can light up the lamps.
[3]
Both set ups have a source of energy. In A, it kinetic energy from a moving palm is converted to electrical
energy. In B, chemical from the battery is converted to electrical energy.
4.
Define potential difference.
[1]
Potential difference (p.d.) is the amount of electrical energy converted to other forms of energy
when a unit of charge passes through a component.
5.
A student observed two difference circuits. In both circuits, the light bulbs used are identical and
the dry cells used are identical.
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Evergreen Secondary School
Secondary Two Science(Physics)
Circuit A
Circuit B
He observed that brightness of the light bulbs in Circuit A is dimmer that the light bulb in circuit B.
a) Explain why is this so? (hint: use the energy distributed per unit charge)
[2]
Both circuits have the same amount of energy per unit charge supplied by the battery. In circuit A,
the energy per unit charge from the source is distributed to two lamps, thence each lamp get lessa
amount of energy per unit charge as compare to circuit B. Therefore, the lamps in circuit A are
dimmer.
b) In circuit A, if the potential difference measure across each lamp is 2 V, what is the e.m.f. of the
battery?
[1]
e.m.f = 2 + 2 = 4 V. (note: All p.d.in the circuit comes from the e.m.f.)
c) What is the potential difference measure across each the lamp in circuit B?
4 V (from part B, the emf is 4 V. All e.m.f. is given to the only component in the circuit)
end
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