## 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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I needed application of light waves and sound waves to the society at large but it was impossible for me to find

This was really helpful for quick revision right before exams .

Good Bt No Electricity

Page 2 is all about Electricity.