KCL Section 4: Reflection (Waves and photons)

Question 1

Reflective surfaces cause waves to change __________: specifically, waves will leave the surface at the _______ angle to the normal but in a ________ direction.

Answer 1

Reflective surfaces cause waves to change direction: specifically, waves will leave the surface at the same angle to the normal but in a different direction.

Question 2

Give examples of applications of the pulse-echo technique

Answer 2

Bats
Dolphins
Sonar
Radar
Ultrasound
A-scans (amplitude scans)

Question 3

An air traffic control system sends out a pulse of radio waves that are reflected by a jumbo jet. The reflection is picked up by the radio dish 0.007 seconds after the emission of the pulse. How far away is the plane?

Answer 3

distance = speed * time 
s = t * v
v = speed of light = 3*10^8
s= 3*10^8  *  0.007 = 2.7 * 10^6
s = 2100km
Remember the wave has travelled there and back!
2100 / 2 = 1050km

Question 4

What is needed for the pulse echo technique to work?

Answer 4

Short pulses (mean that the pulse doesn’t interfere with the echo)
Short wavelengths (less diffraction of the wave, so a more precise measure of where the object/boundary is)