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Electromotive Force
- The e.m.f of a source is the electrical potential energy transferred to other forms, per coloumb of charge that passes through the source.
- The difference between p.d and e.m.f is that p.d is the difference in electrical potential energy transferred to other forms between two points where as e.m.f is the electrical potential energy transferred to other forms that passes through the source.
Current-voltage graph of a metallic conductor
In AS/A-level Physics, current-voltage graph is important to learn.
- As long as temperature stays constant. The graph of a metallic conductor is a straight line passing through the origin.
- This shows that I is directly proportional to V.
- If you double the voltage, the current is doubled and so the value of V/I is always the same.
Current-voltage graph of a semiconductor diode
- There is almost no current when the voltage is applied in the reverse direction. The reverse diode has a very high resistance.
- In the forward direction the current increases very rapidly. The forward diode has a very low resistance.
- The diode conducts only when it is forward-biased. When the diode is reverse-biased there is no current.
Current-voltage graph of a filament lamp
- The graph is a curve as shown.
- Doubling the voltage produces less than double the current.
- This means that the value of V/I rises as the current increases.
- As the current increases, the metal filament gets hotter and the resistance of the lamp rises.
- This is because as the temperature increases the ions vibrate more making it more difficult for the electrons to pass.
Equations to learn
- I=Q/t and 1 amp=1 coloumb per second
- V=W/Q and 1 volt =1 joule per coulomb
- P=VI and P=I^2 x R
- V=IR or R=V/I
- R=‘rho’L/A
- P=IV
- P=I^2 x R and P=V^2/R
- P=W/t
- E.m.f=W/Q or I(R+r)
This is the end of the topic!