Forces and Motion
What is required to create a couple and what is the equation for torque?
Two equal, antiparallel forces acting to produce a turning effect- no translational motion occurs
Torque of a couple = one of the forces × perpendicular distance between them
What are the units and S.I. base units of impulse and momentum
Momentum: kgms-1 (for both)
Impulse: kgms-1 and Ns
What is the energy change of an proton passing through a potential difference of 1V
1 eV as a proton has a charge of +1.6x10-19 C and E = QV
Explain the principle of superposition
If two or more waves of the same type overlap, then the resultant wave can be found by adding the displacements of the individual waves
What experiment proves that light is a wave and which proves that light is made of particles
Wave: Young's double slit experiment
Particle: Electroscope/ Photoelectric effect
How does the velocity of a ball thrown upwards vary between initial pitching and maximum height?
Vertical: Starts with initial velocity (u) decelerates at 9.81 ms-2 until V(vertical)= 0 at maximum vertical displacement
Horizontal: V(horizontal) is constant (assuming negligible air resistance)
What are the characteristics of a pair of forces due to Newton's 3rd law
-Equal magnitude
-Opposite direction
-Same type of force
-Act on different bodies
Explain the IV characteristic graph of a lamp.
As V increases, R increases so I is lower than it should be if V ∝ I
What does it mean if a transverse wave is polarised and what does this do to the wave?
All oscillations are in one plane- polarisation decreases intensity
What is threshold frequency
The minimum frequency of radiation that will result in the emission of electrons
Explain all of the conditions for an object to be in equilibrium
- All coplanar forces must be balanced / F(net) = 0 /All forces form a closed polygon of forces
-Sum of clockwise moments = sum of anticlockwise moments (net moment = 0)
Explain limits of proportionality and elasticity
Before reaching its elastic limit, all stored elastic potential energy completely released when the load is removed. (elastic deformation)
After elastic limit is reached, energy goes into plastically deforming the object
After the limit of proportionality is exceeded, load is no longer directly proportional to the extension (still elastic behaviour)
If I have a cell with internal resistance r Ω and I plot a graph of the output potential difference against the current in the circuit as the resistance of a variable resistor is changed, how do I find the internal resistance and the EMF.
Ɛ= V+Ir ⟹ I(-r) + Ɛ = V
so emf is the y intercept and the internal resistance is the negative of the gradient
Why do pressure variations decrease as a sound wave moves away from its source?
As the wave moves away from the source, energy is spread out over a larger area meaning that the intensity (Power/area) decreases.
Since Intensity∝(Amplitude)2 the amplitude decreases meaning that the maximum pressure is decreased.
Give a reason for why the term Ek max used in Einstein's photoelectric equation
It represents how electrons may collide with each other and loose energy while being liberated, thus emerging with less than their maximum possible kinetic energy
How would you find the pressure on the bottom of a ships hull?
P= F/A. Archimedes' Principle: Upthrust = weight of displaced liquid = Ahρg.
P= Ahρg/A ⟹ P= hρg
(Note: A is the area of the bottom of the ship)
What are the rules for springs in series and parallel explaining the ideas behind them.
Parallel: k1 + k2... = kT
Sum of forces on each of the springs = total input force
Extension of all springs is equal
Series 1/k1 + 1/k2... = 1/kT
Sum of extensions of each of the springs = total extension.
Force on each spring is constant.
(derivations come from substituting F=kx into the added term in each case and and canceling the constant factor)
if two sources of emf (Ɛ1 and Ɛ2, Ɛ1>Ɛ2,) are in series with each other in a circuit, but the polarities are opposite, what is the overall available emf?
What law describes this?
Ɛ1 - Ɛ2
Described by Kirchhoff's 2nd Law
How are stationary waves formed?
Interference between incident and reflected waves of the same type, amplitude and frequency.
Constructive interference forms antinodes and destructive interference forms nodes.
Why is ultraviolet light more suitable for causing electrons to be liberated than visible light
It has a higher frequency therefore a higher photon energy (more likely to have a greater photon energy than the work function of the surface)
Why do objects with more mass reach a higher terminal velocity than those with a lesser mass?
Fd ∝ v2 and W=mg for Fd to be equal and opposite to W, v needs to be larger if m is larger.
If I know the mass of a gun, how fast it travels backwards after shooting and the mass of one bullet how would I work out how far the bullet would go into an object with a constant resistive force of F N. (assuming negligible air resistance and that the gun is fired straight at a target, parallel to the ground)
Conservation of Momentum to work out velocity of bullet.
Work out kinetic energy of bullet.
Use W=Fd with force F, leading to Ek =Fd to work out the distance the bullet travels into the object
How could a potential divider be set up such that output potential difference increases when light intensity increases.
Use a light dependant resistor and measure Vout across the fixed resistor
If light moves from a more to a less optically dense material what can happen depending on the angle of incidence.
If sin θ = n2/n1 then θ is the critical angle and the angle of refraction is 90
if sin θ > n2/n1 the total internal reflection occurs
if sin θ < n2/n1 then wave bends away from the normal according to n1sinθ1 = n2sinθ2
In a photocell, if incident radiation has a constant intensity but increased frequency (from a frequency>work function) how does the current change.
Current decreases.
Each photon has more energy, so for the same intensity, less photons per second are incident on the plate. Since it is a one-to-one interaction, less electrons are emitted per second.