In everyday speech we refer to 'charging' our phone or 'having no charge'. This is incorrect in physics, as charge is conserved and not used up.
Instead, we are using electrical energy (the ability to make charges move!). We get billed for the units we consume of electrical power over a given time.
Power (in any form) is defined as the rate at which work is done or energy is changed:
\(P={W\over t}\)
In electrical circuits, it's often simpler to use \(P=IV\) (to avoid going via three other equations!).
With practice, you will become fluent in deciding which of the following to use:
\(P=IV\)
\(P=I^2R\)
\(P={V^2 \over R}\)
Use quizzes to practise application of theory.
START QUIZ!
Which circuit has the brightest bulb?
The pd across the bulb in C is 6V the others are all less.
Which circuit has the brightest bulb?
PD across the bulbs in D is 2x all the others.
Which circuit has the brightest bulb?
D has 2x the pd of C and A and C has 0V across the bulb
In which 2 circuits are the red bulbs of equal brightness
Bulbs in B and D have same pd
What is the order of brightness of these bulbs
D takes all the current, 2/3 goes through A, 1/3 through B, 1/6 through C.
Calculate the power dissipated in the bulb
Power = V2/R
Calculate the power dissipated in the bulb
I = 6/3 = 2A
P = I2R = 4 x 2
Calculate the power dissipated in the bulb
P = V2/R = 36/2
If the switch is closed which bulbs get brighter?
resistance in circuit gets less so current is more PD across C increases.
PD across B gets less
current through A increases
How much of Electrical power have you understood?
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