A Level Physics Practice Exam

What is the number of complete waves emitted from a source with a wavelength of 600 nm in 0.01 μs?

1. 1 * 10^6

2. 5 * 10^6

3. 2 * 10^14

4. 3 * 10^14

The correct answer is: 5 * 10^6

To find the number of complete waves emitted from a source, we start with understanding the relationship between the speed of a wave, its frequency, and its wavelength. The formula to use here is: \[ v = f \cdot \lambda \] where \( v \) is the speed of the wave (for light in a vacuum, approximately \( 3 \times 10^8 \) m/s), \( f \) is the frequency, and \( \lambda \) is the wavelength. Given a wavelength of 600 nm (which is equivalent to \( 600 \times 10^{-9} \) m), we can first calculate the frequency of the wave: \[ f = \frac{v}{\lambda} = \frac{3 \times 10^8 \, \text{m/s}}{600 \times 10^{-9} \, \text{m}} \] Calculating this gives: \[ f = \frac{3 \times 10^8}{600 \times 10^{-9}} = \frac{3 \times 10^8}{6 \times 10^{-7}} = 5 \times 10^{14} \, \text{Hz} \