Exam Style questions Physics

All topics

Explain the Photoelectric effect (3 marks)

• Ek = hf - o(work function)

• If photons must have energy greater than or equal to the work function.

• Electrons are removed from metal surface

Define Potential difference [1 mark]

• Work done in transferring 1C of charge between 2 points in a circuit

Why would a rechargeable battery require a low internal resistance?

• Battery must be able to deliver a high current

• Low resistance reduces energy loss

• More efficient

An electron has speed ‘v’ it’s kinetic energy is doubled, what is its new speed?

root2v

An object of mass ‘m’ is travelling with a constant resultant force ‘F’ and velocity ‘v’, what is its work done?

mv²/2

Which quantity is conserved in an inelastic collision?

momentum

Using Newtons laws, explain how a propellers thrust allows a ship to maintain constant momentum [4 marks]

• N1L, Force on Ship = Drag on ship (const velocity)

• N2L, Force needed to change waters momentum (F= ma)

• N3L, Force from propeller = Reaction force from water (thrust produced)

A ship produces bubbles to save fuel while maintaining a constant momentum. Explain how this effects thrust and drag [3 marks]

• Drag decreases more than thrust

• For a constant momentum drag = thrust

• Propeller can work at less rotations per second and maintain the same momentum (as when system is off)

• Therefore engine uses less fuel

A suitcase weighing 200 N is placed on a weighing scale in a lift. The scale reads 180 N when the lift is moving. Therefore the lift must be:

Moving up with a decreasing velocity

A battery has an emf of 5.30 V and negligible internal resistance. 1. (a)  State what is meant by an emf of 5.30 V for this battery. [1 mark]

• The energy is transferred from kinetic to electrical energy

• 5.3J to transfer 1C of charge between two points

Suggest why young’s double slit equation should not be used to calculate wavelength [1 mark]

• Equation only valid when screen distance is much greater than slit separation

Explain properties waves must have to superpose and form a large stationary wave

• Must have same speed

• Must be moving in opposite directions

• Must have same wavelength

The string is replaced with one that has 9 times the mass per unit length of the original string. All other conditions are kept constant, including the frequency of the vibration generator and the tension in the string. Deduce the harmonic observed

[3 marks]

• Refer to equation f # 1/mew

• Third harmonic observed

• Frequency is 1/3 of previous number

Distinguish between longitudinal and transverse waves. [2 marks]

• Oscillations of longitudinal waves are parallel to energy transfer/Perpendicular for transverse

• Transverse waves can be polarised

The frequency of the first harmonic of a wire fixed at both ends is 300 Hz. The tension in the wire is now doubled. What is the frequency of the first harmonic after this change?

• f² # T

• Ans: 420hz

Explain how light from the diffraction grating forms a maximum on the screen [3 marks]

• Light waves from the grating undergo diffraction and overlap

• They arrive at screen with zero phase difference

• At the screen they superpose

  Explain what is meant by modal dispersion in an optical fibre. [2 marks]

• Spreading of pulse

• due to different paths taken by waves through optical fibre

Explain, with reference to refractive index, why the pulse of red light has a shorter transit time than the pulse of blue light. [2 marks]

• n = c/cs

• Red light has a smaller refractive index

• Therefore a greater velocity

• Travel distance is equal so red has a shorter transit time

Which change decreases the fringe separation?

A decreasing the separation between the two slits

B increasing the distance between the slits and the screen

C using monochromatic light of higher frequency

D using monochromatic light of longer wavelength

• w = ld/s

• C

Explain why an electron antineutrino, rather than an electron neutrino, is produced during β − decay. [2 marks]

• Lepton number must be conserved

• Electron has lepton no. 1

• Antineutrino has lepton no. -1

Describe the process that occurs when the positron collides with this lepton. In your answer you should identify the lepton in the molecule of water. [3 marks]

• Annihilation

• Particles are completely destroyed

• Gamma photons travelling in opposite directions produced as energy must be conserved

• Particle is an electron

What are the products when a free neutron decays?

• p + e- + v(bar)

The π + decays to produce a positron and an electron neutrino. Show how the conservation laws apply to this decay. [2 marks]

• Charge conserved as e+ and pion have charge 1

• Lepton no. conserved as e+ and v have a sum of 0

The K+ decays to produce an anti-muon and a muon neutrino. Explain how strangeness applies in this decay [2 marks]

• Weak force decay so strangeness can change by +1, 0, -1

• anti muon and neutrino are leptons

• Strangeness not conserved

Write an equation for a K+ decay that involves only hadrons [2 marks]

• K+ —> pi+ + pi0

Discuss the nature of hadrons. Your answer should include:

• the identifying properties of hadrons

• the structure of a hadron in each class

• a discussion of the stability of free hadrons

[6 marks]

• Hadrons contain quarks

• Hadrons interact via strong force

• Baryons 3 quarks/antiquarks

• Mesons 1 quark and 1 antiquark

• Hadrons typically unstable (include example of free meson decay)

• only stable hadron is a proton

What is the role of the mercury vapour in a fluorescent tube? [1 mark]

• Emits UV photons after excitation or ionisation

What is the de Broglie wavelength when the particle has a kinetic energy of 4Ek? [1 mark]

• l/2