AQA A Level Physics

What is the ideal resistance of an ammeter?

Zero

What is the ideal resistance of an voltmeter?

Infinite

State and explain how more cells in a circuit can be added to make the lamp light at normal brightness for a longer time.

- Cells must be added in parallel

- Because less power from each cell

- Without increasing terminal potential difference

After moving the non ideal voltmeter across a different component, explain why the sum of the voltmeter readings do not equal the emf of the battery

- Current in circuit changes

- Because the resistance in the circuit changes

Suggest one possible disadvantage of using the fifth-order maximum to determine N.

Peak is less defined

Explain why a fixed resistor is used in the circuit

- To limit the current

- To prevent overheating of the cell

Advantage of using superconductors in electrical transmission

- Zero resistance/resistivity

- Reduce heat/energy transfer

- Reduce power loss in cables

Disadvantages of using superconductors in electrical transmission

- Difficult to maintain low temperatures over long distances

- Must be kept at critical temperature

Explain how light from the diffraction grating forms a maximum on the screen

- Light from the slits overlap and undergo diffraction

- Path difference is a whole number wavelength

- Arrive at screen in phase

- Undergo superposition

Explain what is meant by modal dispersion in an optical fibre.

- Spreading of pulse (as parts of pulse take different times to travel through the fibre)

- Due to different paths through the optical fibre (due to entering the fibre at different angles)

Conditions required for total internal reflection to occur

- The light must be travelling from a more dense medium to a less dense medium

- The angle of incidence must be greater than the critical angle

What are fibre optics?

Fibre optics use total internal reflection to send high speed light signals over long distances.

What does the cladding do?

- Protects the core from damage

- Has a lower refractive index from the core so total internal refraction can occur at the boundary

- Prevents cross talk between touching fibres

What does absorption do?

- Causes the signals to lose energy which reduces the amplitude

- Signal boosters are used

How to reduce absorption?

Can be reduced if cladding and item are straight

How can modal dispersion be mitigated?

- By using thin core and repeater

- Smaller change in refractive index between core and cladding

- By using a step index fibre

- Regions of the core have different refractive indices so have different critical angles

- Gradual reflections and signals kept in the core and controls the speed the light is travelling at so signal arrives more clearly at the end

What causes material dispersion?

- Different wavelengths of light

- Overcome by using monochromatic light and signal repeaters

Definition of a photon

A massless "packet" or a "quantum" of electromagnetic energy

Definition of annihilation

The destruction of a particle-antiparticle pair when they collide and convert their mass into two gamma-ray photons

Definition of pair production

The creation of a particle-antiparticle pair when a high-energy photon spontaneously converts its energy into mass

Why is the proton the most stable baryon?

- It is the lightest baryon

- Radioactive decay occurs when heavier particles decay into lighter particles

- A decay of the proton would therefore violate the conservation of baryon number

Strange particle characteristics

- Are produced through the strong interaction

- Decay through the weak interaction

- Are produced in quark-anti quark pairs

- Strangeness is conserved in every interaction except the weak interaction

Definition of threshold frequency

The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal

Definition of threshold wavelength

The longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal

Definition of work function

The minimum energy required to release a photoelectron from the surface of a metal

Definition of stopping potential

The potential difference required to stop photoelectron emission from occurring

Definition of simple harmonic motion

Periodic motion where the acceleration of the particle is proportional to but in the opposite direction to the displacement

Explain what happens to light within a bent optical fibre.

- Angle of incidence on core-cladding boundary decreases

- And will now be less than the critical angle

- Some of the light will be reflected into the cladding

Explain why a wave might not refract

It is perpendicular to the boundary

Definition of a progressive wave

A wave that transfers energy from one point to another without transferring the medium itself

Difference in amplitude between the progressive and stationary waves

- Progressive waves: all points have the same amplitude in turn

- Stationary waves: each point has a different amplitude depending on the amount of superposition

Principle of superposition

When two or more waves with the same frequency arrive at a point, the resultant displacement is the sum of the displacements of each wave

Definition of resonance

When the frequency of the applied force to an oscillating system is equal to its natural frequency, the amplitude of the resulting oscillations increases significantly

Definition of damping

The reduction in energy and amplitude of oscillations due to resistive forces on the oscillating system

Explain why thinner cores reduce modal dispersion

Smaller range in path lengths

Explain why variation in amplitude occurs

- Waves superpose and are in phase

- Moving away from phase introduces a path difference and the waves are out of phase so the amplitude decreases

Explain why the amplitude of the waves will gradually increase as the wavelength increases

- Path difference gets closer to one wavelength

- Amplitude will get larger as waves are in phase

State Hooke's Law

The extension is directly proportional to force applied up to the limit of proportionality.

State which feature of this graph confirms that this rubber is elastic.

No permanent extension - the rubber returns to it original length

State the limit of proportionality

- The point at which the graph is no longer linear

- Where extension is no longer proportional to the force applied

Definition of ultimate tensile stress

The maximum stress a material can withstand before it begins to weaken and subsequently breaks

How to correct Chromatic Aberration

Use a diverging lens to change the direction of the refracted rays

How to correct spherical aberration

Use a parabolic mirror

Continuous spectrum

Light spectra created when photons of all wavelengths are emitted

Emission spectrum

Light spectra created when photons are emitted by excited electrons in a hot gas

State one limitation that applies to the pendulum when the time period equation is used.

Amplitude of the bob is small

How is energy lost in a pendulum?

Energy is lost to the surroundings in overcoming air resistance

Explain where the fiducial mark should be placed.

At the equilibrium since the mass moves with the greatest speed

State and explain how the student was able to determine the accurate shape of the graph in the region where the amplitude is a maximum.

Student decreased intervals between readings where A is a maximum

Under what condition would resonance on a bridge become dangerous?

- Bridge has natural frequency

- If the driving force is equal to natural frequency of structure there is resonance

- Vibrations of large amplitude produced

- Could cause damage to structure

Explain how fringes are formed from a double slit.

- Path difference: even number of half wavelengths

- Phase difference is an even number of pi

- Waves meet in phase

- Resulting in constructive interference

Forces in nucleus

- Electrostatic repulsion forces the protons in the nucleus apart

- The strong nuclear force holds all of the nucleus together

Features of the strong nuclear force

- The strong force is highly repulsive at separations below 0.5 fm

- The strong force is very attractive up to a nuclear separation of 3.0 fm

- The maximum attractive value occurs at around 1.0 fm, which is a typical value for nucleon separation

- The equilibrium position, where the resultant force is zero, occurs at a separation of about 0.5 fm

What is the equilibrium position of protons

The equilibrium position for protons, where the electrostatic repulsive and strong attractive forces are equal occurs at around 0.7 fm

Explain how data supports the hypothesis that a third particle is produced during beta minus decay.

- There is missing energy

- Missing energy carried off by third particle

Explain why there is minimum energy in pair production.

The incident photons must have a minimum energy equal to the rest mass energy of the particle and corresponding antiparticle it produces

Suggest two measures which engineers might adopt in order to reduce the size of the oscillations of a bridge

- Stiffen the structure by reinforcement

- Install dampers or shock absorbers

Explain what is meant by forced vibrations.

Vibrations are forced when periodic force is applied

Explain why the period of a trapeze changes when an acrobat lets go of the bar.

- Period shorter

- Centre of mass of acrobat was lower than that of bar

- Effective length of pendulum is lower

Describe a suitable procedure to measure the amplitude of a pendulum.

- Use a set square with edge made vertical and ruler

- Measure Ar from either side of the displaced bob

Definition of diffraction

Spreading out of waves when going through a gap or around a gap

Suggest why Young's double slit equation should not be used to determine the wavelength.

Equation only valid if slit screen distance is a lot greater than slit separation.

How does single slit before the double slit make the light coherent for fringes to be seen?

Single slit acts as a single source diffracting light to both slits and the path lengths between the single and double slits are constant.

State the meaning of the term frequency of a wave.

Number of complete waves passing a point in one second

Explain where the damping is the greatest in the oscillation of a bob.

- At the equilibrium position

- Where the bob is at the centre of motion and experiences the most air resistance

Describe the pattern formed on the screen by a single slit

- Central maxima with lower intensity maxima on either side

- Central maximum twice as wide as other maxima

Describe the interference pattern that is seen on a white screen from white light entering a double slit.

- Central white fringe showing range of colours

- Violet closest to centre

- Red furthest from centre

Suggest how stationary waves are formed in the microwave oven.

- Waves are reflected from the oven wall

- And superpose with wave travelling in opposite direction

Explain why most microwave ovens contain a rotating turntable on which the food is placed during cooking.

Position of the antinode continually changes

Absorption spectrum

Light spectra when photons are absorbed by electrons in a cool gas