Current Electricity
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A concise overview of current electricity, covering key concepts such as resistance, resistivity, emf, internal resistance, potential dividers, and kirchhoff's rules. It explains charge flow, electric current, and the behavior of free electrons in a wire. Formulas for resistors in series and parallel are included, along with a discussion of resistance networks and the effects of temperature on resistance. The document also touches on electrical power, energy, and common electrical symbols, making it a useful resource for students learning about basic electrical circuits and principles.
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2025/2026
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Current Electricity
Resistance
E.M.F and internal resistance
Potential round a circuit
Free electron motion in a wire
The free electrons in a metal have three distinct velocities associated with them: (a) a random velocity ( about 10^5 ms-1) (b) a velocity with which electrical energy is transferred along the wire (about 10^8 ms-1) (c) a drift velocity of the electrons as a whole when a current flows through the wire (this depends on the applied voltage but is usually a few mms-1^ for currents of a few amps in normal connecting leads).
Potential divider
Kirchhoff’s rules (1)
- Kirchhoff's rules
Resistance networks (1)
Twelve resistors in the form of a cube.
The problem is to find the resistance (R) between the points A and B on each cube. Each arm of the cube has a resistance r.
We can take any path through the network between the points A and B. Such a path could be ACDB.
IR = i/3 r + i/6 r + i/3 r = I 5/6 r Therefore: Total resistance (R) = 5/6 r