AQA Physics A Unit 2
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- Created on: 24-05-13 13:52
Define the Young Modulus for a Material
Stress/Strain, assuming the limit of proportionality has not been exceeded.
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Define Strain
Extension per unit length of a solid when deformed.
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What is the unit for stress?
Pascals (Pa)
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What is the Yield Point? (2)
*This is when the material suddenly starts to stretch without any extra load. * The Yield Point is the stress at which a large amount of plastic deformation takes place with a constant or reduced load.
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What is the unit for Strain?
No unit.
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Why must the core of an optical fibre be narrow? (2)
*To prevent multipath dispersion *Less light is lost *Increased chance of TIR *Better quality signal *Less refraction out of the core
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Explain why some waves can be polarised and others cannot. (2)
*Polarisation restricts the vibrations to one plane by absorbing the vibrations at right angles to this plane. *Longitudinal waves cannot be polarised because the vibrations have to take place for energy to be transmitted.
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What is the elastic limit? (2)
*Where the material starts to behave plastically. *From this point onwards, the material would no longer return to its original length/shape once the stress was removed.
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What is plastic deformation?
Deformation of a solid beyond its elastic limit.
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Define Stress
Force per unit area of cross-section in a solid perpendicular to the cross section.
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What are the properties of a progressive wave? (4)
*Travel though space carrying energy *Carry energy through space via vibrations * It has wavelength, frequency and velocity *The wave velocity, V, is given b V= frequency x Wavelength
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Define: Couple
A pair of equal and opposite forces acting on a body but not along the same line.
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What happens if the single slit is too wide? (4)
*Each part of it produces a fringe pattern.*Which is displaced slightly from the pattern due to adjacent parts of the single slit *As a result the dark fringes become narrower than the light fringes.*Contrast between light and dark fringes is lost
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What is phase difference?
The fraction of a cycle between the vibrations of two vibrating particles, measured in degrees or radians.
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What is the limit of proportionality?
The limit beyond which, when a wire or spring is streched, its extention is no longer proportional to the force that stretches it.
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What is the fundamental mode of vibration?
The pattern of stationary waves on a string when it vibrates at its findamental (i.e. lowest possible) frequency
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Define elastic limit
The point beyond which a wire is permanently stretched.
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How does light from a laser differ from non-laser light? (2)
*Laser light is highly monochromatic (You can specify wavelength to within a nanometre, Conves lenses can focus it to a very fine spot.) *Convenient source of coherent light (You don't need to use a single slit)
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What are the characteristics of elastic deformation?
*The material returns to its original shape once the forces are removed.
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What is superposition?
The effect of 2 waves adding together when they meet.
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What is the refractive index?
(Speed of light in a free space) / (Speed of light in a substance)
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What is refraction?
The change of direction of a wave when it crosses a boundary where it changes speed.
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What is the principle of moments?
For an object in equilibrium, clockwise moments about any point = anticlockwise moments about that point
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What is the period of a wave?
The time taken for onc complete cycle of a wave to pass a point.
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What is Newton's second law?
F=MA
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What is Newton's first law?
An object remains at rest or in uniform motion unless acted on by a resultant force
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What is the drag force?
The force of fluid resistance on an object moving through the fluid.
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What is the density of a substance?
Mass per unit Volume of the substance.
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Define amplitude
Maximum displacement of a vibrating particle. For a transverse wave, it is the distance from the middle to the peak of the wave.
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Define Hooke's Law
Hooke's law states that the force needed to stretch a spring is directly proportional to the extension of the spring from its natural length.
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State the characteristics of longitudinal waves
Particle vibration/oscillation direction is the same as the of propagation/energy transfer.
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Which class of wave, longitudinal or transverse, can be polarised?
Transverse waves
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State the characteristics of transverse waves
Particle vibration or oscillation direction is perpendicular to the direction of propagation or energy transfer.
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What does the amount of diffraction of a wave depend on? (2)
*Wavelength of the waves *Size of the gap they're passing through
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An Apple falls from a tree. Using Newton's laws of motion, explain why the apple accelerates first then reaches a terminal velocity.
*Weight initially greater than air resistance *Hence acceleration (because resultant force is downwards) *Air resistance increases with speed *Until air resistance equals weight, the resultant force =0 *Apple moves at a constant velocity (1st Law)
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What is fringe separation?
The distance from the centre of a bright fringe to the centre of the next bright fringe.
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How is a bright fringe formed? (2)
*The light from one slit reinforces the light from the other slit *The light waves from each slit arrive in phase with eachother.
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What is terminal speed?
The maximum speed reached by an object when the drag force is equal and opposite to the force causing the motion of the object.
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What is total internal reflection?
A light ray travelling in a substance is totally internally reflected at a boundary with a substance of lower refractive index, if the angle of incidence is greater than the critical angle.
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What is Ultimate tensile stress?
Tensile stress needed to break a solid material.
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What are progressive waves?
Waves which travel thought a substance or through space if electromagnetic
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What is a node?
A fixed point in stationary wave pattern where the amplitude is zero.
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What is efficiency?
The ratio of useful energy transferred (or useful work done) by a machine or device to the energy supplied to it.
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Define Cycle
The interval for a vibrating particle (or a wave) from a certain displacement and velocity to the next time the particle (or the next particle) has the same displacement and velocity.
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What is the critical angle?
The angle of incidence of a light ray must exceed the critical angle for total internal reflection to occur.
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Define coherence
Two sources are coherent if they emit waves with a constant phase difference.
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Define centre of mass
The point through which a single force on the body has no turning effect.
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Define stress
Force per unit area of cross-section in a solid perpendicular to the cross section, measured in Pascals (Pa)
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What is an antinode?
A point of maximum oscillation
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Why can't sound be polarised?
Because it is a longitudinal wave, there are no vibrations perpendicular to the direction of travel.
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How is a dark fringe formed?
The light from one slit cancels the light from the other slit. The light waves from the two slits arrive 180 degrees out of phase
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What are stationary waves?
Wave pattern with nodes and antinodes formed when two or more progressive waves of the same frequency and amplitude pass through eachother.
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What is interference?
Formation of points of cancellation and reinforcement where coherent waves pass through eachother.
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What is the unit for the Spring Constant?
N/m
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What is monochromatic light?
Light with a single wavelength
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A single slit diffraction pattern is produced on a screen using a laser. Describe how the pattern would change if light of a longer wavelength was used.
The maxima would be further apart
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State two ways in which the appearance of the fringes would change if the slit was made narrower.
*Wider/increased separation *Lower intensity
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The speed of light is given by c = f λ. State how each of these quantities will change, if at all, when light travels from air to glass.
c= decrease. f= constant. λ= decrease
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Explain the difference between a progressive transverse wave and a stationary transverse wave in terms of amplitude. (2)
*In a stationary wave: The amplitude varies from zero at the nodes to a maximum at the antinodes. *In a progressive wave, the amplitude is the same for all particles
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Explain the difference between a progressive transverse wave and a stationary transverse wave in terms of phase difference between two particles. (2)
*For a stationary wave: Phase difference is equal to mπ where m is the number of nodes between the two particles. *For a progressive wave, phase difference is equal to 2πd/λ where d=distance apart and λ is the wavelength.
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Explain the differences between a progressive transverse wave and a stationary transverse wave in terms of frequency. (2)
Stationary waves: All particles except at the nodes vibrate at the same frequency. Progressive wave: All particles vibrate at the same frequency.
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Give two reasons why optical fibres used for communications have a cladding.
*To protect the core *To prevent crossover of signal *To increase the critical angle *To increase the rate of data transfer
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What is multipath dispersion?
*This occurs in a wide core because light travelling along the axis of the core travels a shorter distance per metre of fibre than light that repeatedly undergoes total internal reflection.
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Give two reasons why a diffraction grating arrangement is more suitable for the accurate measurement of the wavelength of light that the two-slit interference arrangement.
*Brighter images * Large angles *Sharper (or narrower) lines
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Other cards in this set
Card 2
Front
Define Strain
Back
Extension per unit length of a solid when deformed.
Card 3
Front
What is the unit for stress?
Back
Card 4
Front
What is the Yield Point? (2)
Back
Card 5
Front
What is the unit for Strain?
Back
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