2017 - WAEC Physics Past Questions and Answers - page 3

A saturated vapour is one which is in a dynamic equilibrium with its own liquid.

This is a type of constructive interference. When two waves of equal amplitude are interfering constructively, the resulting amplitude is twice as large as the amplitude of an individual wave.

= A + A = 2A

The 3rd overtone for an open pipe has 5 antinodes and 4 nodes.

Comparing the given equation with the wave equation:

\(Asin(kx - \omega t)\), we have that A = 10 which is the amplitude of the wave.

Diffraction refers to the various things that occur when a wave encounters an obstacle. This bending of the wave after it passes a small gap is an example of diffraction.

\(\eta = \frac{1}{sin\theta}\)

\(1.5 = \frac{1}{sin\theta}\)

\(sin\theta = \frac{1}{1.5} = 0.667\)

\(\theta = sin^{-1}(0.667) = 41.835°\)

\(\approxeq 41.8°\)

For the 4th harmonic, \(L = 2\lambda\)

\(4m = 2\lambda \implies \lambda = \frac{4m}{2}\)

=\(2m\)

Recall, \(v = f\lambda\)

\(1 = f \times 2 \implies f = \frac{1}{2}\)

= 0.50Hz

The number of images formed = \(\frac{360}{n}\) where the value gotten is odd

else, = \(\frac{360}{n} -1\).

Solving, we have that \(\frac{360}{20} = 18\)

Hence, the no of images formed is 18 - 1 = 17.

Given, image size = 3U

object size = U

focal length = 10cm

lens to object distance = \(\frac{focal length \times object size}{image size}\)

= \(\frac{10 \times u}{3u} = 3.33\)

distance between image and object = 10 + 3.33 = 13.33cm