Exam Question Answer Structure Flashcards
Explain (using the graph) whether the object obeys Hooke’s Law
- constant gradient
- passes through zero
- extension is proportional to force
What is the centre of gravity
the point at which all the weight of an object can be assumed to act
State a simple method to test the centre of gravity of an object
balance the object on a finger/pivot at this point and see if it stays balanced and level
Suggest why the drag is so much greater than the Stoke’s law force
because Stoke’s law relies only on laminar flow
Temperature and viscosity
as the temperature increases the viscosity lessens so the ‘material’ flows more and is easier to spread
State what is meant by work done
work done = force x distance moved in direction of the force
State what is the difference between the stress above and below …
when below the stress is tensile, when above the stress is compressive
Describe what is meant by plane polarised light
light only oscillates in one plane/direction, all other light is blocked if not oscillating in that plane, the plane includes the direction of travel
Explain longitudinal waves
oscillations occur parallel to the direction of wave propagation/travel creating compressions and rarefactions
What is ultrasound
frequency greater than 20000 Hertz
Why is ultrasound emitted in pulses
so it has time between pulses for the previous pulse to return before the next one is sent; so we know which echo is from each pulse
property of x-rays
ionising
difference between x-rays and ultrasound
- x-rays transverse, ultrasound longitudinal
- x-rays travel in a vacuum, ultrasound doesn’t
- x-rays electromagnetic, ultrasound mechanical
Explain what is meant by unpolarised
- oscillations occur in every directions
- perpendicular to the direction of wave travel
Explain what is meant by a photon
a concentrated packet of electromagnetic energy
Explain what is meant by threshold frequency
the minimum amount of energy (frequency) needed to release the photon from the surface of the metal. Only at this frequency or above will photons be emitted, one photon is absorbed by one electron, E = hf
State what is meant by drift velocity
mean velocity of charge carriers
State what is meant by refraction
as light passes a boundary through substances of different densities it causes a change in speed which causes a change in direction
Total Internal Reflection
when the incident angle of light is greater than the critical angle all light is refracted so much it stays inside a tube/ball
Superposition
when two waves pass through each other and the amplitudes sum (constructive) or subtract (destructive) creating nodes and antinodes
Diffraction
spreading out of waves as they pass through a gap - maximum diffraction occurs when the size of the gap is similar to the size of the wavelength
Explain why microwave/ other radiation could be dangerous
human body contains water so would gain heat
is ionising
Photoube/Photoelectric effect
- electrons in metal plate absorb photon energy
- then they flow round a circuit to positive charge
- photon energy depends on frequency, photons must have more than the threshold frequency
- one photon can transfer energy to a single electron
- light with a greater intensity supplies more photons per second so more electrons can be emitted per second causing a greater current
Why use a data logger
- higher sampling rate
- ensure the readings are simultaneous
- take more readings in a shorter time interval
Explain 2 precautions the student should take to ensure accurate results
- switch off between readings so no heaing effect
- no zero error
- no parallax error
- no systematic error
Conserved in a reaction
- charge
- momentum
- baryon number
- mass
Faraday’s law of induction
induced EMF is proportional to the rate of change of flux linkage
