Waves Flashcards
State what is meant by monochromatic.
-Single wavelength (or frequency)
State what is meant by coherent.
-(waves/source(s) have) constant phase difference
The laser in a double slit interference test is replaced by another laser emitting visible light with a shorter wavelength.
State and explain how this will affect the spacing of the maxima on the screen. (2 marks)
- Maxima will end up closer together
- Quote fringe spacing eq. spacing is proportional to wavelength so as wavelength decreases, fringe spacing decreases.
State TWO requirements for two light sources to be coherent. (2 marks)
- Same wavelength or frequency
- Constant phase difference
Transverse waves:
oscillations are are at right angles to the direction of travel and energy transfer
Longitudinal waves:
oscillations are along the same direction as the direction of travel and energy transfer.
How to count up the number of maxima/lines produced?
Always treat the first maxima line as ZERO (0) then count up.
Eg if there is nine lines, total number would be 8 as first one is zero
(use trapezium rule y0 y1 analogy)
What do the symbols mean in fringe spacing eq :
w=(Lambda.D)s
Lambda- Wavelength
s: ‘The slit spacing’
w: All maxima added up and divided by the length (fringe spacing) e.g 8 maxima/0.16m = 0.020m
D: Distance from slits to screen (basically the laser length)
A narrow beam of monochromatic red light is directed at a double slit arrangement. Parallel
red and dark fringes are seen on the screen shown in the diagram above.
Describe how the appearance of the fringes would differ if white light had been used
instead of red light (3 marks)
-central (bright) fringe would be white (due to waves of all colours meeting at midpoint in same phase)
-(dark) fringes would be closer together because white light has a shorter wavelength
-bright fringes wider
(generally would form blue on LHS and red on RHS) due to white light containing all colours
State two ways in which the appearance of the fringes would change if the slit was made
narrower. (2 marks)
- Wider/increased separation
- Lower intensity
Characteristics of white light used in a slit experiment:
- Central bright fringe
- Blue colour formed on far LHS maxima
- Red colour formed on far RHS maxima
How to show that beams cannot be observed over a certain order:
dsintheta=nlambda
Solve for n and let sintheta = sin90
work out the value for n, e.g (1.67x10^-6xsin90/590x10^-9)
=2.83
Therefore 3rd order or higher isn’t possible
State and explain what happens to the value of angle θ for the first order beam if the
wavelength of the monochromatic light decreases (2 marks)
- Angle gets smaller
- Because path difference gets smaller
what is d in dsintheta=nlambda
d=1/N(Number of slits per metre)
Describe the necessary procedure in order to obtain an accurate and reliable value
for the wavelength of the laser light.
Your answer should include details of all the measurements and necessary
calculations. (6 marks)
- Use dsintheta=nlambda
- Measure appropriate angle (first order beam minimum)
- Protractor to measure angle
- For accuracy, use protractor with 0.5degrees or less intervals
- Obtain d by 1/Lines per mm x10^3 (x10x100)
- Rearrange equation for lambda=dsintheta/n to obtain wavelength
- Check/repeat for different distances (D)
- Use spectrometer
- Measure theta for different orders
Electromagnetic waves are similar in nature to wave A.(transverse)
Explain why it is important to correctly align the aerial of a TV in order to receive the
strongest signal. (2 marks)
- (transmitted radio waves are often) polarised
- aerial must be aligned in the same plane (of polarisation) of the wave
Amplitude (2 marks)
- The maximum displacement
- From the equilibrium position
The wave travels to the right.
Describe how the vertical displacement of the knot varies over the next complete cycle (for transverse wave) (3 marks)
A continuous wave of the same amplitude and frequency moves along the rope from the
right and passes through the first wave. The knot becomes motionless.
Explain how this could happen. (3 marks)
- (vertically) downwards
- then upwards
- down (¼ cycle) to equilibrium position
- Stationary wave formed
- By superposition
- knot is at a node / waves always cancel where the node(knot) is
When stating the characteristic features of waves, what should you mention?
The motions of oscillation towards direction of wave travel/ propagation/ energy transfer
Other than electromagnetic radiation, give one example of a wave that is transverse.
- Surface of water in ripple tank
- Rope
Daylight passes horizontally through a fixed polarising filter P. An observer views the light
emerging through a second polarising filter Q, which may be rotated in a vertical plane
about point X
Describe what the observer would see as Q is rotated slowly through 360 (2 marks)
- variation in intensity between max and min (or light and dark)
- two maxima (or two minima) in 360° rotation
State one application, other than in education, of a polarising filter and give a reason for its
use. (2 marks)
Camera: Reduces glare/enhances image
Wavelength of a wave
Least distance between two adjacent vibrating particles with the same displacement and velocity at the same time
Figure 1 represents a stationary wave formed on a steel string fixed at P and Q when it is
plucked at its centre.
Explain why a stationary wave is formed on the string ( 3marks)
-Progressive waves travel from the centre to the ends of the string (nodes) and reflect back
-two (progressive) waves travel in opposite directions along the string
-Superposition/(interference) occurs
(waves have same frequency,wavelength, and amplitude)
