·

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!