Home PHYSICS TOPIC 2: CURRENT ELECTRICITY | PHYSICS FORM 2

TOPIC 2: CURRENT ELECTRICITY | PHYSICS FORM 2

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PHYSICS FORM TWO FULL NOTES
Electric current is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes. In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and resistance by Ohm’s law. The standard abbreviations for the units are 1 A = 1C/s.
Current Electricity
Define current electricity
Current
electricity is a fundamental quantity and is the amount of charge
passing a given point in a circuit divided by the time required for the
passage of charges.
Electrical current (I) =quantity of charge (Q)/Time (t)
I =Q/t
Q = I.t
Electric current = rate of flow of charge
= (the number of charge carried per second x charge of a single electron)
From this definition the SI unit of an electric current is I =Columbus(C)/Second (s)
I = c/s = A
This unit is commonly known as an Ampere (A). Other units are milliamperes (mA), kilo amperes (KA) and Microampere (mA).
Their equivalents to the ampere are as follows:
1A = 10-3mA
1A= 10-6mA
1KA = 1000A
So
when a steady electric current of 1A is flowing in a circuit a coulomb
of charge passes a given point of the circuit per second.
An instrument used to measure electric current is called an Ammeter.
In
this chapter we shall study the sustained movement of electric charge
called electric current. To maintain a steady flow of electricity charge
capable of moving and ways of causing them to move. Secondly, there
must be a closed path around which the charge moves. This path is known
as electric circuit.
A coulomb
This is the quantity of electricity, which passes a given point in circuit in 1 second when a steady current of 1 ampere flows.
In
electric current there are flows of electrons through the conductor.
Electrons are negatively charged while protons are positively charged.
The motion of the charge through the circuit transfers energy from one
point to another. This means that the actual directors of an electric
current are opposite to the conventional direction.
Uses of current electricity
Current electricity is mainly used for:
  1. Cooking
  2. Lighting
  3. Communication; and
  4. Heating among many other uses
Different Sources of Current Electricity in Everyday Life
Identify different sources of current electricity in everyday life
All sources of electric currents work by converting some kind of energy into electrical energy. The two basic sources are:
  1. Batteries e.g. Mobile phone battery, car dry cell batteries and also car alternator.
  2. Generator
Batteries convert chemical energy into electrical energy. While generators convert mechanical energy into electrical energy.
Other
sources of electric energy include water (hydroelectric power), water
currents i.e. ocean waves, solar energy and wind energy.
Hydroelectric
power is very reliable except in time of severe drought. This is
because electricity is generated from water in dams and waterfalls,
which depends on rainwater. Turbines are used to generate electricity
form falling water.
Solar
cells trap and convert solar energy into electric energy. Space ships
and satellite use solar cell to convert sun light into electricity.

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