Exam questions for 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
State one safety precaution that should be taken while using a laser.
eye/safety signs/suitable safety goggles
The laser 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.
maxima closer together as shorter path width
Using the wave theory, explain how the pattern of bright and dark patches is formed. (double slit)
narrow single slit gives wide diffraction
State two requirements for two light sources to be coherent.
same wavelength and constant phase difference
Explain the formation of fringes from the double slit experiment
where light from the two slits overlaps (or superposes)
bright fringes are formed where light (from the two
slits) interfere constructively/crest meets crest)
dark fringes are formed where light (from the two slits)
cancels (or interferes destructively/trough meets crest)
the light (from the two slits) is coherent
Describe how the pattern would change if light of a longer wavelength was used.
maxima further apart
Explain how the appearance of the first-order beam can be used to deduce one piece of
information about the gases that make up the outer layers of the star.
black lines reveal the elements within the star
Describe the necessary procedure in order to obtain an accurate and reliable value
for the wavelength of the laser light.
measure between more than one order (eg 2 θ)
• measure θ for different orders (for average λ not average angle)
• check or repeat/repeat for different distances (D)
• use of spectrometer
• use large distance to screen (D)
• protractor with 0.5 degree (or less) intervals
• graphical method: plot sin θ against n (gradient = λ/d)
State and explain one advantage associated with a smaller diameter core.
less light is lost
• better quality signal
Explain why it is important to correctly align the aerial of a TV in order to receive the
strongest signal.
(transmitted radio waves are often) polarised
aerial (rods) must be aligned in the same plane (of polarisation / electric field) of
the wave
The wave travels to the right.
Describe how the vertical displacement of the knot varies over the next complete cycle starts at equilibrium
(vertically) downwards (¼ cycle to maximum negative displacement)
then upwards (¼ cycle to equilibrium position and ¼ cycle to maximum
po itive di placement)
down (¼ cycle) to equilibrium position/zero displacement and correct
reference to either maximum positive or negative displacement or correct
reference to fractions of the cycle
Explain why a stationary wave is formed on the string.
(progressive waves travel from centre) to ends and reflect (1)
two (progressive) waves travel in opposite directions along the string (1)
waves have the same frequency (or wavelength)
Explain how a stationary wave is formed. Then describe the key features of the stationary wave shown in the figure above.
4 nodes where there is no movement/zero amplitude
• 3 antinodes where amplitude is maximum
• wavelength 0.80 m
• end antinodes in phase/middle and ends in antiphase
• between node and antinode, amplitude of oscillation increases
• waves reflect off the clamp (and the rod)
• waves travelling in opposite directions superpose/add/interfere
• wave have same wavelength and frequency (similar amplitude)
• always cancellation at nodes/always constructive superposition at antinodes
• energy is not transferred along string
