1. Which of the following quantities from a point source decreases according to an inverse square law (∝ 1/r²)?

2. If you double the distance from a small point light source, the measured intensity becomes:

3. A point charge gives an electric field magnitude E0 at distance r. What is the field at r/3 (ignoring vector direction)?

4. A point source's intensity drops to 1/16 of its original value. By what factor has the distance from the source changed?

5. A small isotropic point light source emits 500 W of radiant power. Calculate the irradiance (W·m⁻²) at a distance of 2.0 m. Show your working.

6. A detector reads 120 lux at 1.5 m from a bulb. At what distance from the bulb will the detector read 30 lux? Show your working and give the answer in metres.

7. Two identical point charges produce an electric field magnitude E at a distance of 2.0 cm from one charge. What is the field magnitude at 8.0 cm from that charge (express as a multiple of E)? Show working.

8. Two identical lamps are both 2.0 m from a detector; each produces 50 lux at that distance. One lamp is moved to 4.0 m while the other remains at 2.0 m. Calculate the new total illuminance at the detector. Show your working.

9. A satellite experiences gravitational acceleration g = 9.80 m·s⁻² at a planet's surface radius R. If the planet's radius were increased to 1.20 R (mass unchanged), what would the new surface gravity be? Show your working and give g to three significant figures.

10. A 100 W point sound source produces an intensity I0 at 3.0 m. What intensity will be measured at 10.0 m? Express your answer as a fraction of I0 and calculate the decimal. Show working.