Physics Module 4 Waves

Question 1

1. Progressive Wave

Answer 1

An oscillation that travels through matter (or in some cases a vacuum) and transfers energy from one place to another, but not matter. When a progressive wave travels through a medium, the particles in the medium move from their original equilibrium position to a new position. The displaced particle experiences a restoring force from its neighbours and returns to its original position.

Question 2

2. Longitudinal Wave

Answer 2

A wave in which the medium is displaced parallel to the direction of energy transfer. The oscillations about the equilibrium are parallel to the direction of travel of the wave. Often called compression waves because as they travel they create a series of compressions and rarefactions. Example: Sound waves, P-Waves.

Question 3

3. Transverse Wave

Answer 3

A wave in which the medium is displaced perpendicular to the direction of energy transfer. The oscillations about the equilibrium are perpendicular to the direction of travel of the wave. Transverse waves have peaks and troughs where the oscillating particles are at a maximum displacement from their equilibrium. Example: Surface water waves, electromagnetic waves, S-Waves, waves on a string.

Question 4

4. Displacement

Answer 4

s. Distance from the equilibrium position in a particular direction; a vector, so it can have either a positive or a negative value. Measured in metres, m.

Question 5

5. Amplitude

Answer 5

A. Maximum displacement from the equilibrium position. Measured in metres, m.

Question 6

6. Wavelength

Answer 6

λ. Minimum distance between two points in phase on adjacent waves. For example, from peak to peak, from rough to trough, from compression to compression, between identical points. Measured in metres, m.

Question 7

7. Period

Answer 7

T. Time taken for one oscillation or time taken for wave to move one whole wavelength past a given time. Measured in seconds, s. T = 1 / f.

Question 8

8. Phase Difference

Answer 8

Difference between the displacements of particles along a wave or on different waves. Measured in degrees or radians; a whole oscillation is 360o or 2π radians. If oscillations are ‘in step’, they are described as in phase. Phase difference is an integer multiple of 360o or 2π radians. If oscillations are completely ‘out of step’, they are described as in antiphase. Phase difference is an odd integer multiple of 180o or π radians.

Question 9

9. Frequency

Answer 9

f. Number of wavelengths passing a given point per unit time. Measured in Hertz, Hz (s-1). f = 1 / T.

Question 10

10. Speed of a Wave

Answer 10

v (or c). Distance travelled by a wave per unit time. Measured in ms-1. v = f λ.

Question 11

11. Oscilloscope

Answer 11

Used to determine the frequency of a wave. The screen shows a graph of p.d. against time for any signal fed into it. Each horizontal square on the screen represents a certain time interval, the ‘timebase’. Also known as cathode ray oscilloscope or CRO.

Question 12

12. Reflection

Answer 12

When a wave changes direction at a boundary between two media, remaining in the original medium. The arrow on the ray shows the direction of energy transfer. Frequency and wavelength does not change. The ‘Law of Reflection’ states that the ‘angle of incidence equals the angle of reflection’, both measured from the normal.

Question 13

13. Diffraction

Answer 13

When waves pass through a gap or travel around an obstacle, they spread out. Diffraction is greatest when the size of the gap is similar to the wavelength.

Question 14

14. Ripple Tank

Answer 14

A ripple tank is a shallow glass tank of water used in schools to demonstrate the basic properties of waves.

Question 15

15. Intensity

Answer 15

I. Radiant power passing through a surface per unit area. I = P / A (= P / 4πr2 for a sphere). Measured in watts per square metre, Wm-2. Intensity α Amplitude2.

Question 16

16. Electromagnetic Spectrum

Answer 16

The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies. They are all transverse and travel through a vacuum at 3.00 x 108 ms-1. Electromagnetic radiation refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space, carrying energy.

Question 17

17. Order of Magnitude

Answer 17

A class in a system of classification determined by size, typically in powers of ten.

Question 18

18.RadioWave

Answer 18

λ= >106 to10-1 m.

Question 19

19. Microwave

Answer 19

λ = 10-1 to 10-3 m.

Question 20

20. Infra-Red

Answer 20

λ = 10-3 to 7 x 10-7 m.

Question 21

21. Visible

Answer 21

λ = 7 x 10-7 (red) to 4 x 10-7 (violet) m.

Question 22

22. Ultraviolet

Answer 22

λ = 4 x 10-7 to 10-8 m.

Question 23

23. X-Ray

Answer 23

λ = 10-8 to 10-13 m.

Question 24

24. Gamma Ray

Answer 24

λ = 10-10 to 10-16 m.

Question 25

25. Polarisation

Answer 25

The phenomenon in which oscillations of a transverse wave are limited to only one plane or along one direction. When transverse waves reflect off a surface they become partially polarised; this means more waves oscillate in one plane, but it is not completely plane polarised.

Question 26

26. Plane Polarised

Answer 26

Description of a transverse wave in which the oscillations are limited to only one plane.

Question 27

27. Refraction

Answer 27

When a wave changes direction at a boundary between two media as it passes from one medium to another. Whenever a wave refracts, there is always some (partial) reflection off the surface.

Question 28

28. Refractive Index

Answer 28

n. No units. n = c / v. c is the speed of light in a vacuum = 3.00 x 108 ms-1. v is the speed of light through the material in ms-1.