Section 2 - Waves and Optics Exam Questions Flashcards
Waves, Optics.
Define monochromatic (1)
Single wavelength
Define coherent (1)
Constant phase difference
State a safety precaution when using a laser (1)
Do not look into laser
State and explain the effect of using a laser with a shorter wavelength on the maxima spacing in Young’s double slit (2)
Maxima closer together
use w=𝜆D/s
Use wave theory to explain how the fringe pattern is formed (4)
Slits act as coherent sources Waves diffract at slits Waves superpose Bright patches: constructive Dark patches: destructive
State two requirements for two light sources to be coherent (2)
Same wavelength
Same phase
Explain how Young’s double slit arrangement produces interference fringes, refer to width of first slit and coherence of second slits (6)
Narrow single slit gives wide diffraction to ensure that both second slits are illuminated
Paths to second slits are of constant length giving constant phase difference
Light diffracted at slits and overlap and interfere
Where path lengths differ by whole number of wavelengths, constructive interference occurs producing a bright fringe
If Young’s double slit was carried out with red light and then with white light, how would the two differ? (3)
Central fringe would be white
Dark fringes would be closer together
Side fringes are spectra
State two ways a diffraction pattern on single slit would change if the slit became narrower (2)
Increased separation
Lower intensity
State and explain what happens to angle θ in λ = d sin θ when wavelength decreases? (2)
Angle θ gets smaller
As path difference gets smaller
How can the appearance of a first order beam from light from a star be used to deduce information about the outer layers of the star? (1)
Absorption spectrum reveals the composition of the star’s atmosphere
Why will total internal reflection occur when light ray travels from water into glass? (refractive index) (1)
TIR only occurs when ray travels from higher n to lower n
What is the name for the part of an optical fibre that is around the core? (1)
Cladding
State and explain an advantage of a smaller diameter core (2)
Reduce multipath
Which would cause poor resolution
State one application of optical fibres and its benefit to society (2)
Communications
Improved transmission of data
Explain why optical fibres used for communication need to have cladding (2)
Keeps signal secure
Keeps most light rays in
State and explain two physical properties of the light produced by a laser which makes it different to that produced by a lamp (4)
Monochromatic
Waves of single wavelength
Coherent
Waves produced in constant phase
Explain how glass cladding around the optical fibre’s core improves the security of data being transmitted through it and give a reason (3)
Light doesn’t enter cladding so can’t pass across from one fibre to a neighbouring fibre
Fibres without cladding can allow light to pass between fibres when scratched or linked by moisture
Personal data must be transmitted along fibres where there is no danger of light leakage
Define longitudinal wave (1)
A wave with a direction of vibration that is parallel to the direction of propagation of the wave
Define transverse wave (1)
A wave with a direction of vibration that is perpendicular to the direction of propagation of the wave
Explain why it is important to correctly align the aerial of a TV to receive the strongest signal (2)
Transmitted radio waves are often polarised
Aerial rods must be aligned in the same plane of the wave
Define amplitude of a wave (1)
The maximum displacement of the wave from the equilibrium position
Describe the vertical displacement of a point over the next cycle of a transverse wave (3)
Vertically downwards 1/4 cycle to negative amplitude
Then upwards 1/4 cycle to equilibrium point and 1/4 cycle to positive amplitude
Down 1/4 cycle to equilibrium position
Why could the point become motionless if a wave of the same amplitude frequency moves along from the opposite direction? (2)
Stationary wave formed
by superposition
Point is at a node
If there are two polarising filters inbetween an observer and light, if one is turned about 360 degrees, what would the observer see? (2)
Variation in intensity between max and min
Two maxima in 360 degree rotation
Give three examples of waves that are transverse (2)
Electromagnetic radiation
Surface of water
Rope
State one application of a polarising filter and a reason for its use (2)
Camera
Reduce glare
A microwave transmitter directs waves towards a metal plate. A detector is placed between and moved along a line, what causes the maxima and minima of waves detected? (3)
Superposition
reflection from metal plate
two waves of same frequency
travelling in opposite directions
How can a guitarist raise the fundamental frequency of vibration in their string? (1)
Tighten the string
State and explain the features of Young’s Double Slit (7)
Light source - multiple wavelength of visible light
Filter - selection of single wavelength, production of monochromatic source
Single slit - diffraction - Allows single source to strike 2 slits
Double slit - source entering is coherent due to previous step
Screen is large distance from double slit - measurable outcome and reduction in size of error
Describe the structure of a step-index optical fibre outlining the purpose of the core and cladding (3)
Core is transmission medium for electromagnetic waves to progress by total internal reflection
Cladding has a lower refractive index to allow total internal reflection to occur
Cladding offers protection from scratching that could lead to light loss
Blue light has a higher refractive index fibre than red light, explain how this difference results in a change in a pulse of white light by the time it leaves the fibre (2)
Blue travels slower than red due to greater refractive index
Red reaches the end of the fibre before blue leading to material pulse broadening
Discuss two changes to reduce material pulse broadening of white light(2)
Monochromatic source so speed is constant
Shorter repeaters so pulse is reformed before significant broadening occurs
Suggest an experiment to demonstrate the wave nature of sound (1)
Diffraction through a door
Which observation helped to conclude that the speed of sound does not depend on frequency, when measured by firing a gun? (2)
Sound of gun is a mixture of frequencies
All sound reaches observer at the same time
Which quantities are changed when monochromatic light passes from air into glass? (1)
Speed and wavelength only
A student stretches a guitar string using unit masses to find fundamental frequencies at certain tensions, why might the actual frequency for higher tensions be different than predicted? (2)
Reducing diameter with string is stretched
Lower mass per unit length so frequency is higher
Of the electromagnetic waves, which has the greatest energy? (1)
Gamma rays
An endoscope contains two bundles of optical fibres
Name each bundle and explain its use in viewing inside the body (4)
Coherent bundle with fixed arrangement at each end
Used to transmit images
Non-coherent bundle with random arrangement of fibres
Used to transmit light into the body
Slits in front of microwave transmitter, receiver is moved along a line behind the slits. Explain why the signal strength falls to a minimum at certain points (3)
Path difference for two waves
Gives rise to a phase difference
Destructive interference occurs
Slits in front of microwave transmitter, receiver is moved along a line behind the slits. Explain why the minimum intensity between two points is not zero (2)
Intensity decreases with distance
One wave travels further than the other
An aerial wire is hung between two masts, when the wind blows stationary waves can be formed. Explain how stationary waves are produced and why only certain frequencies form (4)
Wind produces a wave that travels along the wire
Waves are reflected at each end
Incident and reflected waves interfere
Only certain frequencies since fixed ends have to be nodes
