WaPNoL 1

Question 1

Amplitude

Answer 1

Maximum displacement from the equilibrium position.

Question 2

Frequencey

Answer 2

Number of waves passing a point per second (or number of wave oscillations per second).

Question 3

Period

Answer 3

Time for one complete wave oscillation. Period = 1/frequency (T = 1/f)

Question 4

Wavelength

Answer 4

Distance between two consecutive points that are in phase (e.g. successive peaks).

Question 5

Wave Equation

Answer 5

Wave speed (ms-1) = frequency (Hz) × wavelength (m)
v = fλ

Question 6

Phase

Answer 6

The fraction of a cycle one oscillation lags (or leads) another, often expressed as an angle.(phase difference): “In phase” means phase difference = 0°, “In anti-phase” means phase difference = 180 degrees

Question 7

Wavefront

Answer 7

A wavefront is a line on which all the points are in phase (e.g. All peaks of a wave).

Question 8

Transverse wave

Answer 8

The particles oscillate at right-angles to the direction of energy transfer (propagation). e.g. light.

Question 9

Longitudinal wave

Answer 9

The particles oscillate backwards and forwards in the direction of energy transfer (propagation). e.g. sound.

Question 10

Speed of light

Answer 10

Speed of light in a vacuum, c = 3 ×10^8 ms-1. (Note: Speed of light in air = 3 × 10^8 ms-1) Note: For any electromagnetic wave in a vacuum, the wave equation becomes c = fλ

Question 11

Interference

Answer 11

The combination of two or more waves of the same type.

Question 12

Coherence

Answer 12

Sources are coherent if they maintain a fixed phase-relationship

Question 13

Principle of Superposition

Answer 13

“The resultant displacement of 2 or more waves at a point is equal to the VECTOR sum of their individual displacements at that point.”

Question 14

Maxima

Answer 14

Waves meet with 0° phase difference, resulting in constructive superposition occurs producing a point/region of maximum amplitude.

Question 15

Minima

Answer 15

Waves meet with 180° phase difference, resulting in destructive superposition occurs producing a point/region of minimum amplitude.

Question 16

Stationary wave

Answer 16

Stores energy. Caused when 2 identical waves pass through each other in opposite directions (caused by either two sources pointing at each other, or one wave reflecting back on itself).   
Contains nodes (not moving/minimum oscillation) and antinodes (maximum oscillation).      
(Important: Node-to-node distance = λ/2)   Between nodes particles are in phase and have different amplitudes. Particles either side of a node oscillate 180 degrees out of phase.

Question 17

Path Difference

Answer 17

Difference in distance travelled by two waves to a single point. Used to calculate the phase-difference between the two waves. If the path-difference is λ/2 (or odd number of λ/2) the two waves arrive ‘180 degrees out of phase’. If the path-difference is a multiple of λ they arrive in phase.

Question 18

Wave Transmission

Answer 18

When wave energy is (partially or completely) carried through, out of or into a media.

Question 19

Wave Reflection

Answer 19

When a wave rebounds off an interface: Angle of incidence = Angle of reflection.

Question 20

Wave refraction

Answer 20

Change in speed of a wave as it passes into a different medium causing a change in wavelength. (Causes bending of the direction of the wave if it is not already moving along the normal.)

Question 21

Snell’s Law

Answer 21

n1sinθ1 = n2sinθ2 (Also: n1/n2 = v2/v1 = sinθ2/sinθ1)

n1 = refractive index for medium 1, 
θ1 = angle from normal made in medium 1,
v1 = speed in medium 1 
n2 = refractive index for medium 2, 
θ2 = angle from normal made in medium 2,
v2 = speed in medium 2

Question 22

The critcal angle

Answer 22

The angle of incidence that causes an angle of refraction = 90° (i.e. greatest angle of incidence that allows a ray to exit a medium.) Common equation used is: C = sin-1(n1/n2) (where the ray is travelling from medium 1 into 2).

Question 23

Total internal reflection

Answer 23

Occurs inside a medium when a ray fails to exit (transmit) and reflects back in because the angle of incidence is greater than the ‘critical angle’

Question 24

Optical centre

Answer 24

A point in the lens through which rays will pass without deviation.

Question 25

Principle axis

Answer 25

A line that passes normally (at 90°) through the optical centre of a lens.

Question 26

Focal length

Answer 26

Displacement along the principle axis from optical centre of a lens to the real/virtual focal point.

Question 27

Power of Lens

Answer 27

Power = 1/focal length Unit: dioptre (m-1)

Question 28

Converging lens

Answer 28

Parallel rays pass through the lens and converge to meet at a real focal point. (Note: Converging lenses have a positive power and a positive focal length)

Question 29

Diverging lens

Answer 29

Parallel rays pass through the lens and diverge from a virtual focal point. (Note: Diverging have a negative power and a negative focal length)

Question 30

The Lens Equation

Answer 30

1/u + 1/v = 1/f [Note: Real images have positive v, virtual images have negative v] (where u = distance parallel to principle axis from object to optical centre) (where v = distance parallel to principle axis from optical centre to image)

Question 31

Pulse echo techniques

Answer 31

Pulse of speed, v, is emitted, travels a distance, x, reflects off an object and travels back in a time, t. Equation can be used to find v, d or t: v = 2x/t (or x = vt/2).

Question 32

Scan resolution

Answer 32

Detail recorded is limited by wavelength & pulse time. (Shorter the better to avoid poor focus from diffraction spread and from interference between outward & return pulses)