Page 124 - Physics Form 5 KSSM_Neat

3.3 Electromotive Force (e.m.f.)

and Internal Resistance

Electromotive Force
There are various sources of electromotive force, e.m.f. like
electric generators, dynamos, batteries and accumulators.
KEMENTERIAN PENDIDIKAN MALAYSIA
Photograph 3.3 shows several sources of e.m.f.

The electromotive force (e.m.f.), Ԑ is the energy
transferred or work done by an electrical source to Lead-acid accumulator
move one coulomb of charge in a complete circuit.

Ԑ = E
Q
where Ԑ = electromotive force
E = energy transferred / work done
Q = the amount of charge flowing
–1
The S.I. unit for e.m.f. is volt (V) or J C .
Dry cell
(Alkaline cell)

Photograph 3.4 shows a dry cell that can supply Lithium-ion battery
1.5 J of electrical energy for each coulomb of charge in Photograph 3.3 Sources of e.m.f.
a complete circuit.

Info GALLERY

e.m.f. of a dry cell = 1.5 V
= 1.5 J C –1

A voltmeter has a high resistance.
Thus, the current from a dry
SCAN ME cell through a voltmeter can be
SCAN ME
Video of neglected. The voltmeter reading
Electromotive is the e.m.f. of the dry cell.
Force and Internal
Resistance
Photograph 3.4 A dry cell https://bit.ly/2QJbAR1

114 LS 3.3.1