# Physics Unit 2

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Why do Fibre Optic cables have a small diameter?
To prevent multipath dispersion by where light travelling at different angles will arrive at different times
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What is a scalar?
A value that has only magnitude
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What is a vector?
A value that has magnitude and direction?
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What are examples of Scalars?
Mass, temperature, time, length, speed, energy
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What are examples of Vectors?
Displacement, force, velocity, acceleration, momentum
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What do the gradient and area underneath a velocity/time graph tell us?
Gradient - Acceleration, Area underneath - Distance travelled
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How can velocity be estimated from a curved displacement/time graph?
Draw a tangent at that point and find its gradient
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What is the definition of "density"?
Mass per unit volume
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What is the definition of "centre of mass/gravity"?
The single point that you consider its whole weight to act through
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What factors affect the stability of an object?
Position of centre of mass and size of base
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What is the "principle of moments"?
For a body in equilibrium, sum of clockwise moments = sum of anticlockwise moments
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What is a "couple"?
A pair of forces of equal size that act parallel to each other in opposite directions
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How can the torque of a couple be calculated?
Torque = Size of One force x Distance between forces
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What is Newton's first law?
The velocity of an object will not change unless a resultant force acts upon it
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What is Newton's second law?
Force = mass x acceleration
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What is Newton's third law?
Every action has an equal and opposite reaction
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What is "Work done"?
The energy that has been changed from one form to another
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What is "Power"?
Amount of energy transferred from one form to another per second, i.e. Work Done per second
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What is Hooke's Law?
Extension of a wire or spring is directly proportional to the applied load up to the limit of proportionality
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What is Elastic Deformation?
The material returns to its original shape once forces are removed - atoms return back to their equilibrium positions
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What is Plastic Deformation?
The material is permanently stretched - some atoms do not return back to their equilibrium positions
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What is Ultimate Tensile Stress?
The maximum stress a material can withstand
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How can Elastic Strain Energy be calculated from a Force/Extension graph?
Area underneath (whilst Hooke's Law is obeyed)
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How can the Spring Constant, K, be calculated from a Force/Extension graph?
Gradient of the line (whilst Hooke's Law is obeyed)
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What is a 'brittle' material?
A material that breaks suddenly under applied force through the appearance of cracks?
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What is a fracture?
The rapid propagation of a crack through a material causing it to break
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What is a 'ductile' material?
The shape can be changed such that it can easily be drawn out into wire form
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What is a 'malleable' material?
A material that can change shape relatively easily under applied force
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What is a progressive wave?
A wave that carries energy from one place to another without transferring any material
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What is the amplitude of a wave?
Maximum displacement from its equilibrium position
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What is the wavelength of a wave?
The distance between two equivalent points on a wave
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What is the period of a wave?
The time taken for one full wave cycle
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What is a cycle?
One complete wave from one peak to the next
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What is the frequency of a wave?
Number of full wave cycles which pass a point per second
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What is reflection?
When a wave is bounced back after it hits a boundary
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What is refraction?
When a wave changes direction as it enters a medium of different density as a result of speeding up or slowing down
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What are the differences between Transverse and Longitudinal waves?
Transverse waves vibrate perpendicular to their displacement whereas Longitudinal waves vibrate parallel to their displacement. Transverse waves have Peaks and Troughs whereas Longitudinal waves have Compressions and Rarefactions
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What is a polarised wave?
A wave that only oscillates in one plane/direction
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What are examples of Transverse and Longitudinal waves?
Transverse - EM Waves, Ripples on water. Longitudinal - Sound, Primary Seismic Waves
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What is Total Internal Reflection and what are the conditions needed for it to happen?
When all the light is reflected back into a material. Happens when the angle of incidence is bigger than the critical angle
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What are the two parts of an optical fibre called?
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What must happen for two light sources to be coherent?
Same wavelength and frequency with a fixed phase difference
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What is Monochromatic light?
Light of a single wavelength
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What points do constructive interference occur?
When the path difference is an integer number of wavelengths
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What is a standing wave?
The superposition of two progressive waves travelling in opposite directions with the same wavelength
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What are the different harmonics?
Fundamental Frequency - Where there are two nodes and one antinode, half wavelength long. Second Harmonic - 3 nodes, 2 antinodes, one wavelength long. Third Harmonic - 4 nodes, 3 antinodes, 1.5 wavelength long
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## Other cards in this set

### Card 2

#### Front

What is a scalar?

#### Back

A value that has only magnitude

### Card 3

#### Front

What is a vector?

### Card 4

#### Front

What are examples of Scalars?

### Card 5

#### Front

What are examples of Vectors?