exam questions paper 1

Question 1

State the conditions for simple harmonic motion.

Answer 1

→ acceleration is proportional to displacement
→ acceleration is in opposite direction to displacement

Question 2

State Ohm’s Law

Answer 2

voltage across a conductor is directly proportional to current flowing through it, provided temperature remain constant

Question 3

State what happens to photoelectrons when V is negative

Answer 3

• electrons lose KE
• fewer electrons have sufficient energy to move across anode
• current decreases

Question 4

What is meant by a coherent source?

Answer 4

→ same frequency / wavelength
→ constant phase difference

Question 5

Which colour of light travels the fastest and why?

Answer 5

RED:
longest wavelength
least bending of light
smaller refractive index

Question 6

Describe two solutions to pulse broadening caused by multi-path dispersion.

Answer 6

→ use monochromatic light so that source has single frequency
→ use monomode fibres

Question 7

Explain what is meant by multi-path dispersion.

Answer 7

• in a core, light can take multiple paths
• this means each beam reaches end at a different time
• causes the pulse to spread out & reduces signal quality

Question 8

Explain what is meant by modal dispersion. Suggest a solution.

Answer 8

• beams enters fibre at different angles
• each beam undergoes TIR a different number of times
• so each beam reaches end at a different time.
• use a narrow core

Question 9

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

Answer 9

→ an e- has a lepton number of -1
→ therefore, an antineutrino (+1) must be produced to conserve lepton number

Question 10

Explain how to vertically polarise a wave.

Answer 10

→ rotate aerial until it is vertical
→ signal received will be max when vertical
as aerial will be aligned with plane polarised wave

Question 11

When is Young’s double-slit equation valid?

Answer 11

when d is much greater than s

Question 12

What is the role of the mercury vapour in a fluorescent tube?

Answer 12

It emits photons of UV light following ionisation or excitation.

Question 13

State one advantage and one difficulty when using superconductors in electrical
transmission over long distances

Answer 13

:) zero resistance
:( difficult to maintain low temperature

Question 14

Explain how Newton’s three laws of motion apply to a ball being swung around on a string in a circle.

Answer 14

→ ball constantly changes direction ∴ velocity is not constant so ball is accelerating as it is acted on by a force
→ F = ma, force on the ball causes the ball to accelerate in the same direction ∴ as force is centripetal, ball’s acceleration is also towards the centre
→ third law: mg is supported by vertical component of tension and centripetal force is supported by horizontal component of tension

Question 15

Explain what is meant by resonance.

Answer 15

→ when frequency of driving force to an oscillating system is equal to its natural frequency
→ amplitude of oscillations increases significantly

Question 16

Explain what happens to the resonance peak as damping is increased.

Answer 16

• peak lowers
• curve broadens & moves slightly to the left

Question 17

Define damping.

Answer 17

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

Question 18

Describe the changes in amplitude for the three types of damping.

Answer 18

• light → decreases exponentially over time
• heavy → amplitude gradually becomes zero (no oscillations)
• critical → amplitude becomes zero in the quickest possible time (no oscillations)