AS Unit 2 Physics Flashcard Deck

Pregunta	Respuesta
What's the difference between a scalar and a vector?	A scalar quantity has only size, while a vector quantity has size and direction.
What name is given to a vector formed by adding vectors together?	The resultant (vector).
If a body is in equilibrium, what is the sum of all the forces acting on it?	0
What is a moment?	A moment is the turning effect of a force around a turning point/pivot. It's the force x the perpendicular distance from the pivot to the line of action of the force.
What name is given to the moment applied by a couple?	Torque
What is the centre of mass of an object?	The single point that you can consider an object's whole weight to act through.
Where should the centre of mass of an object lie so it doesn't topple?	It's centre of mass needs to stay within the object's base.
What's the velocity of an object?	It is the rate of change of displacement.
What's the acceleration of an object?	It is the rate of change of velocity.
What are the 4 suvat equations for constant acceleration?	v = u+ at s = ((u + v) / 2)t s = ut + 1/2at^2 v^2 = u^2 + 2as
What kind of motion does a curved displacement-time graph show?	Acceleration or deceleration
What kind of motion does a straight line on a displacement-time graph show?	Constant velocity
How would you calculate the velocity of an object from its displacement-time graph?	Calculate the gradient
What does the gradient of a velocity-time graph tell you?	The acceleration
How is uniform acceleration shown on a velocity-time graph?	As a straight line
What does the area under a velocity-time graph tell you?	The displacement
How is non-uniform acceleration shown on a velocity-time graph?	As a curved line
State Newton's three laws of motion, and briefly explain what they mean.	1st law - the velocity of an object won't change Unless a resultant force acts on it. This means a body will stay still or move in a straight line at a constant speed unless there's a resultant force acting on it. 2nd law - resultant force = mass x acceleration. This means a larger force acting on an object causes a larger acceleration, and a larger mass means a smaller acceleration for a given force. 3rd law - if an object A exerts a force on object B, then object B exerts an equal and opposite force on object A. This means every action has an equal and opposite reaction.
What's the only force present in free-fall motion?	Weight
What's free-fall motion called when the object is given an initial velocity?	Projectile motion
In what direction does a frictional force act?	The opposite direction to the motion.
What is friction causes by a fluid called?	Drag or fluid friction
What can you say about the frictional forces and the driving forces acting on an object when it reaches terminal velocity?	The frictional forces are equal in size and opposite to the driving force(s).
How does a skydiver reduce his or her terminal velocity?	By using a parachute to increase the drag hey experience.
What's transferred when work is done?	Energy
Power is the rate of doing what?	The rate of doing work (or transferring energy).
What's the principle of conservation of energy?	Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will remain constant.
How is the efficiency of a machine defined in terms of power?	The useful power output divided by the power input.
What is Hooke's law?	The extension of a stretched elastic object is proportional to the load or force applied to it.
What is the formula for Hooke's law, and define all the symbols used.	F = kΔL, where F is the force applied, k is the stiffness constant, and ΔL is the extension/change in length.
What is meant by the elastic limit of a material?	The force (or load) beyond which a material will be permanently stretched.
What is meant by the limit of proportionality for a material?	The force beyond which force is no longer proportional to extension.
What does it mean if a material is deforming elastically?	It returns to its original shape shape/length once the forces acting on it are removed.
What does it mean if a material is deforming plastically?	It is permanently stretched once the forces acting on it are removed.
What is meant by tensile stress, tensile strain, and breaking stress?	- The force applied divided by the cross-sectional area. - The change in length divided by the original length of a material. - The smallest stress that is enough to break a material.
Explain how you would find the elastic strain energy stored by a stretched material using its force-extension graph?	Work out the area underneath the line/curve of the graph up to the extension required.
What is the formula that relates the elastic strain energy, force, and extension of a stretched material obeying Hooke's Law?	Energy stored = 1/2 x FΔL
What are the units of the Young modulus?	Nm^-2 or Pa (Pascals)
Name four values you would need to measure when carrying out an experiment to find the Young modulus of a wire.	Original length, extension, weights/load, diameter of a wire (to find cross-sectional area).
What does the gradient of a stress-strain graph tell you?	The Young modulus of the material tested.
What does the area under a straight stress-strain graph tell you?	The strain energy per unit volume stored in the material.
What is the difference between a material at the elastic limit and the limit of proportionality?	Once beyond the limit of proportionality, a material no longer obeys Hooke's law but will still behave elastically and return to its original shape once the stress is removed. After the elastic limit, a material behaves plastically and will not return to its original shape if the stress is removed.
What is the yield point of a material?	The stress at which a large amount of plastic deformation takes place with a constant or reduced load.
What is a brittle material?	One which doesn't deform plastically, but snaps when the stress on it reaches a certain point.
Do brittle materials obey Hooke's law? Explain.	Yes - the stress-strain graph for a brittle material is a straight line, which shows it obeys Hooke's law.
Give an example of a brittle material.	Ceramics, iron etc.
What is brittle fracture?	When a stress applied to a brittle material causes tiny cracks at the material's surface to get bigger and bigger until the material breaks completely.
How does a wave transfer energy through a medium?	By causing the particles in the medium to oscillate.
What causes a wave to refract?	A change of medium causing the wave to slow down or speed up.
Which of the following measurements can take a negative value? Displacement or amplitude?	Displacement
State what the units of the following properties of waves are measured in: Displacement, amplitude, and frequency.	Displacement - metres (m) Amplitude - metres (m) Frequency - hertz (Hz)
How would you calculate the frequency of a wave, given its period?	Frequency = 1 / period
What does c stand for in the equation c = fλ?	Wave speed
What is the difference between a transverse wave and a longitudinal wave?	In transverse waves, the vibrations are at right angles to the direction of travel, whereas in longitudinal waves the vibrations are along the direction of travel.
Give an example of a transverse and longitudinal wave.	- Electromagnetic waves, water waves, waves on ropes, earthquake shock waves (S-waves). - sound waves, earthquake shock waves (P-waves).
What happens when you put two polarising filters at right angles in front of a beam of light?	No light gets through.
What happens to unpolarised light when it is reflected?	It is partially polarised - most vibrations of the reflected light are in the same direction.
Explain how Polaroid sunglasses reduce glare.	Reflected light is partially polarised. Polaroid sunglasses block out light in the direction in which the reflected light is partially polarised, but let through light vibrating in other directions. This reduces glare without reducing visibility.
Other that polarising sunglasses, give one example of how polarised waves are relevant to everyday life.	Reducing reflections in photography, aligning TV and radio receivers.
What is the refractive index of a material?	It's a measure of the optical density of the material, given by the ratio of the speed of light in a vacuum to the speed of light in the material.
What is the formula for calculating the refractive index of a material, and what does each part of the equation represent?	n = c / c(s), where c is the speed of light in a vacuum, n is the refractive index of the material, and c(s) is the speed of light in the material.
In what way will light bend if it passes at and angle into a medium with a higher refractive index than the material it just left?	It will bend towards the normal.
What do we mean by the critical angle of a boundary of two materials?	The critical angle of a boundary is the angle of incidence at which the angle of refraction is 90 degrees.
Give three advantages of using optical fibres for communication.	More information can be carried, almost no energy is lost (e.g. as heat), no electrical interference, cheap to produce, transmits across long distances very quickly.
What does the principle of superposition say?	When two or more waves meet, the resultant displacement equals the vector sum of the individual displacements.
Describe constructive interference.	When two waves pass through each other and their displacements combine to make a displacement with greater magnitude.
What is total destructive interference?	When two waves pass through each other and their displacements cancel each other out completely.
What is the phase difference of two points on a wave?	The phase difference of two points on a wave is the difference in their positions in a wave's cycle, measured in degrees or radians.
When are two points on a wave exactly out of phase?	When their phase difference is an odd multiple of 180 degrees (or pi radians).
What does it mean for two waves to be in phase?	Two waves are in phase if they have a phase difference of 0 degrees (or a multiple of 360 degrees).
How is a stationary wave formed?	When two progressive waves are travelling in opposite directions with the same frequency (or wavelength) and the same amplitude, their superposition creates a stationary wave.
Does a stationary wave transfer energy?	No
Describe what a resonant frequency of a string is.	A resonant frequency of a string is a frequency at which a stationary wave is formed because an exact number of waves are produced in the time is takes for a wave to get to the end of the strong and back again.
Describe a string vibrating at its second harmonic.	A string is vibrating at its second harmonic if one wavelength fits on the string and here are three nodes and two antinodes.
What sort of waves diffract?	All waves
What sort of gap would you expect to produce the most diffraction?	A gap whose size is roughly the same as the wavelength of the wave being diffracted.
What is monochromatic light?	Monochromatic light is light made up of only one frequency (and wavelength).
What property of laser light means that it will produce a clearer diffraction pattern than white light?	Laser light is monochromatic, which means all the light has the same frequency (or wavelength). If you used non-monochromatic light, such as white light, different wavelengths would diffract different amounts, so the pattern wouldn't be very clear.
What sort of interference is responsible for the bright fringes on a diffraction pattern produced by laser light passing through a single slit?	Constructive interference
What does it mean for two wave sources to be coherent?	Two wave sources are coherent if the waves have the same wavelength and frequency and a fixed phase difference between them.
What is meant by the path difference of two waves?	The amount by which the path travelled by one wave is longer than the path travelled by the other wave.
At what path differences will you see constructive interference?	At path differences which are an integer multiple of the wavelength (nλ).
What must be true of two wave sources if they produce a clear, standard two-source interference pattern?	They must be coherent.
How can you create two coherent sources of sound waves?	Have one amplifier attached to two loudspeakers.
How can you create two coherent sources of light waves?	Have one coherent light source (e.g. a laser) shining through two slits.
What is Young's double-slit formula which links fringe spacing (w), wavelength (λ), distance between slits (s) and distance between slits and screen (D)?	w = λD / s
What's a diffraction grating?	A slide or other thin object that contains lots of little equally spaced slits.
Why is it often better to use a diffraction grating instead of a double-slit set-up?	The fringes produced in a diffraction grating experiment are much sharper than those produced with a double-slit set-up.
What's the zero order line of a diffraction grating experiment?	The zero order maximum is a line of maximum brightness at the centre of a diffraction pattern. It's in the same direction as the incident beam.
What would happen to the interference pattern produced if you increased the wavelength of light transmitted through a diffraction grating?	The pattern would spread out.
Why is a spectrum formed when white light passes through a diffraction grating?	White light is made up of a range of different wavelengths. These spread out by different amounts when they pass through the diffraction grating, forming a spectrum.
Give one use for line spectra in science.	Spectroscopy - analysing the elements present in stars and galaxies.

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