## Electricity and D.C. Circuits

$\epsilon = \frac{W}{Q}$

$V = \frac{W}{Q}$

$I = \frac{Q}{t}$

$R = \frac{V}{I}$ (IMPT: It’s ratio, NOT gradient)

$R = \frac{\rho L}{A}$

Series: $R_{total} = R_{1} + R_{2} + …$

Parallel: $\frac{1}{R_{total}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + …$

$P = VI = I^{2}R = \frac{V^{2}}{R}$

$E = Pt = (VI)t$

## Electromagnetic force and Electromagnetic Induction:

Transformer:

$\frac{V_{p}}{V_{s}} = \frac{N_{p}}{N_{s}}$

$V_{p}I_{p} = V_{s}I_{s}$

Operation of transformer:

- Alternating current supplied to primary coil
- Alternating current causes iron core to magnetise and magnetic field to change
- Magnetic fields follow iron core and link to secondary coil
- Hence, emf is induced in the secondary coil by electromagnetic induction due to the changing magnetic fields

Left hand rule for motor:

Right hand rule for generator/dynamo:

Right hand grip rule: (To determine direction of magnetic field/current)

Ways to increase emf in solenoid:

- Use a stronger magnet
- Increase the speed of moving the magnet
- Increase the number of turns in the coil

Ways to increase emf in a.c. generator:

- Decrease distance between magnet and coil
- Use a stronger magnet
- Increase frequency of rotation of the coil (Double freq. = double max. e.m.f. and halving T)
- Increase number of turns in the coil (Double no. of turns = double max e.m.f.)

## Radioactivity & The Nuclear Atom

Half life: (n is number of half-life)

$$\frac{N_{\text{final}}}{N_{\text{initial}}} = \left( \frac{1}{2} \right)^{n}$$

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Good Bt No Electricity

Page 2 is all about Electricity.