1. Light entered a heavier medium(eg. glass) n2 from n1 which is air. The refractive index of air n1 equals 1. That is, n1=1. The speed of light is 3×10^8 m/s in air. The speed of light dropped to 2×10^8 m/s when it entered n2.

Find n2 without using calculator.

2. Frequency is a measure of how many oscillations an object goes through per second. Period is how many seconds it takes for one cycle. One is the inverse of the other. I.e., T=1/f and f=1/T. A wave(not light, therefore speed is not 3×10^8) has wavelength of 2m takes 10 seconds to move 5 wavelengths. Find its velocity, period, and frequency.

3. A converging lens has focal length of 10cm. An object is placed 5cm away from the lens. Find image distance. Is the image on the same side as the object? or opposite? real or virtual? upright or inverted? What is magnification? Try to sketch diagram for this.