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Section 2: Electricity

a) Units
b) Mains electricity
c) Energy and potential difference in circuits
d) Electric charge

a) Units

Students will be assessed on their ability to:

Examiner's Expectation: 2.1 Students should be able to use the following units during examination: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V), watt (W).

S.NoQuantityDefinitionunitRepresentation of unit
1

Current  (I)

"Flow of charges Or Flow of electrons"

However, if definition is asked in exam then only write the following formula

Current = Charge / time

 Ampere A
2

Electric Charge (Q)

 Definition is beyond IGCSE
What you need to know is that there are two types of charges i) Positive (+) and ii) Negative (-)		 Coulomb C
3

Energy (E)

Energy: Ability to do something.

Note1: There are several forms of energy like sound,light,nuclear etc and all of them are measured in Joules.

Note2:Energy is a scalar quantity ie it has no direction.

 Joule J
4 Work done  (W or E)

Exam definition

Work done = Force x distance moved

Note1: It is a scalar quantity

Note2: whenever work is done energy is always transferred one form to another. Therefore,

Work done = Energy transferred

 Joule J
5 Resistance (R)

Property of an object to resist the flow of electron or current.

However, if definition is required in exam then write its formula in words as shown below

Resistance = Voltage / Current

symbolically, R = V / I

Note1: Resistance in circuits is represented by a rectangular box called resistor.

 resistordefinition

Note2:All materials offer resistance to current.

Objects which are made up of insulating materials like wood or less conducting material like iron have less resistance.

 Ohm Ω
6 Time (t)
 Definition is beyond GCSE. Second s
7 Potential Difference (V)
 electricityunits1 Volt V
8 Power (P)

Rate of doing work or Rate of energy transferred.

However, in exam just write the following formula in words

Power = Work done / time

Watt

or Joule/Second

1 W = 1 J/s

W

or 1 J/S