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A Level Physics - LVI B > Waves and Optics > Flashcards

Flashcards in Waves and Optics Deck (63)
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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 in Youngs double slit experiment (4)

Slits act as coherent sources
Waves diffract at slits
Waves superpose -
Bright patches: constructive - in phase
Dark patches: destructive - 180 degrees out of phase


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
Where path lengths differ by 0.5 x n wavelengths, destructive interference occurs producing a dark 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 narrower together
Side fringes are spectra


State two ways a diffraction pattern on single slit would change if the slit became narrower (2)

Increased separation - see single slit equation
Lower intensity - less light could get through


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


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
(as long as the incident angle is greater than the critical angle)


What is the name for the part of an optical fibre that is around the core? (1)



State and explain an advantage of a smaller diameter core (2)

Reduce multipath dispersion
Which would cause poor resolution


State one application of optical fibres and its benefit to society (2)

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)

Waves of single wavelength
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


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


State one application of a polarising filter and a reason for its use (2)

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)

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
shorter length of string
Use a string of lower mass per unit length


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 distance between repeaters so pulse is reformed before significant broadening occurs


Suggest an experiment to demonstrate the wave nature of sound (1)

Diffraction through a door