Physics Voltage Energy and Power Revision Notes

Revision notes that I created on voltage energy and power for Physics AS :)

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  • Created on: 14-05-11 18:56
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Physics Electrons, waves and photos
Voltage, energy and power
Page 129
Chapter 11
The meaning of voltage
The voltmeter around a power supply will always read the same. This is because the voltmeter
measures the potential difference between two points. The two points will have the start voltage
e.g. 12, and the finish voltage e.g. 0. The difference is therefore 12. The voltage is used up in
the components around the circuit.
As a rule the voltmeter has to be in parallel otherwise it is not measuring the potential
difference.
Electrical energy is transferred to the charge by the power supply. The charge flows around the
circuit, transferring some of its electrical energy to the first component and the rest to the
others.
The voltmeter placed across the power supply measures the electromotive force.
The voltmeter placed across the resistors measure potential difference.
Potential difference is used when charges lose energy by transferring electrical energy to other
forms of energy in a component. Energy transferred per unit charge.
Electromotive force is used when charges gain electrical energy from a power supply or a
battery. Energy transferred per unit charge.

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Physics Electrons, waves and photos
Voltage and energy
Using the example above:
A 12 V power supply give 12 J of electrical energy to each coulomb of charge that passes
through it. Each coulomb of charge dissipates 8 J of energy as heat in the first resistor and 4 J
of energy as heat in the other.
All the energy gained by the one coulomb of charge is transferred to the components in the
circuit.…read more

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Physics Electrons, waves and photos
Electrical power
The rate at which energy is transferred is known as power. Power is measured in watts. It is
defined as:
Power = Energy transferred / Time taken
P = W / t
Where P is the power and W is the energy transferred in a time t.
The rate at which energy is transferred in an electrical component is related to:
1. The current in the component.
2. The potential difference across the component.…read more

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Physics Electrons, waves and photos
Power can be calculated by two equations:
Power = Current 2 x Resistance
P = I 2R
Power = Voltage 2 / Resistance
P = V 2 / R
These two equations can be used to calculate power waster as heat!
Calculating energy
Power = Current x Voltage
Energy = Power x time
Energy = (Current x Voltage) x time
W = I V t
Summary
The term potential difference is used when charges lose energy in a component.…read more

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Physics Electrons, waves and photos…read more

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