A ray of light travels from a medium of refractive index n₁ to a medium of refractive index n₂. If angle of incidence is i and angle of refraction is r, then $\dfrac{\text{sin i}}{\text{sin r}}$ is equal to

1. n₁

2. n₂

3. $\dfrac{\text{n}$2}{\text{n}1}

4. $\dfrac{\text{n}$1}{\text{n}2}

Fuse is an alloy of

1. lead and copper
2. copper and tin
3. lead and tin
4. None of the above

Which of the following is not a representation of electric power?

1. I²R
2. $\dfrac{\text{V}^2}{\text{R}}$
3. VI
4. I²V

(a) Write the two uses of radioactivity.

(b) A crow-bar of length 80 cm has its fulcrum situated at a distance of 10 cm from the load. Calculate the mechanical advantage of the crow-bar.

(c) Why fission nuclei undergo β-decay?