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SS1: PHYSICS – 2ND TERM

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An electric current is the time rate of flow of electric charges along a conductor. An electric current is said to coexist when there is a net flow of electric charge through a region.

Electric current is defined as the time rate of flow of charges along a conductor.

Electric Current (I) = \( \frac{Quantity \; of \; charge}{time} \\ = \frac{Q}{t} \\ = \frac{Coulumbs}{seconds} \)

Quantity of charge, Q = Current x time = It.

The unit of current is Ampere (A).

The current is always measured by an instrument called an ammeter which is placed in series with the circuit.

ammeter2 e1644874556366
Ammeter.

An ammeter is always connected in series along a circuit

ammeter in series

Other smaller currents are measured in milliampere (MA) or microampere (A).

                          milliAmpere = 10-3A

                          microAmpere = 10-6A

Another instrument used for measuring current is a Galvanometer. It is denoted with the following symbol:

Galvanometer
Galvanometer.

Let’s take a look at some examples;

Example 1:

Calculate the current generated when 350 coulombs of charge flow in a circuit for 4½ minutes.

Solution:

Formula: Q = It

Q = 350 C

t = 4½ minutes = 4½ x 60 seconds

= \( \frac{9}{2} \scriptsize \: \times \: 60 \)

= 270seconds

∴ 350 = I x 270

I = \( \frac{350}{270} \)

I = 1.3 ampere (A)

Example 2:

A current of 100mA passes through a conductor for 2 minutes. What is the quantity of electricity transported?

Solution:

Formula: Q = It

I = 100mA = 100 x 10-3 A

t = 2 minutes = 2 x 60 seconds = 120 seconds

Q = ?

∴ Q = 100 x 10-3 x 120

= 12 C

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