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These are the notes of Exam Paper of Physics. Key important points are: Uncharged Capacitor, Initial Charge Acquired, Final Voltage on Capacitor, Final Charge on Capacitor, Rectangular Loop, Uniform Magnetic Field, Magnitude of Velocity
Typology: Exams
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Question 1. (Marks 12)
Consider the circuit shown in the figure, where C 1 = 6.00μF, C 2 = 3.00μF, and ∆ V = 20.0V.
Capacitor C 1 is first charged by closing switch S 1. Switch S 1 is then opened, and the charged
capacitor is connected to the uncharged capacitor by closing S 2.
(a) Calculate the initial charge acquired by C 1
, after S 1
is closed.
(b) Calculate the final charge on each capacitor.
(c) Calculate the final voltage on each capacitor.
Question 2. [Marks 18]
The figure shows a rectangular loop of width w , length l , mass M and resistance R falling through a
region of uniform magnetic field strength B , directed out of the page. The magnitude of the velocity
of the loop at any instant is v. The loop is made from conducting wire.
During the time interval before the top edge of the loop reaches the field, and before any part of the
bottom edge of the loop leaves the field,
(a) State, with reasoning, whether the direction of the induced current I in the loop is clockwise
or counterclockwise.
(b) Derive an expression for the rate of change of magnetic flux through the loop.
(c) Derive an expression for the power dissipated in the loop.
(d) The loop will approach a terminal speed v T. Derive an expression for this speed in terms of
the properties of the loop, the magnetic field strength B , and the acceleration due to gravity g.
Question 4. (Marks 15)
(a) Consider a Young's double slit apparatus in which the centre-to-centre slit spacing is 0.3 0 mm
and the slits-to-screen distance is 0.8 0 m. Two wavelengths of light
λ 1
, λ 2
, illuminate the slits
simultaneously, where
λ 1
= 500 nm and
λ 2
= 600 nm, producing two interference patterns on
the screen. Find the separation (distance) on the screen between the two third-order
interference patterns produced by
λ 1
, λ 2
(b) To maximize collection efficiency by minimizing reflective losses, the surface of silicon (Si)
solar cells can be coated with a thin film of silicon monoxide (SiO).
(i) On the diagram below, representing a SiO coated Si solar cell, sketch in transmitted and
reflected rays, indicating on the sketch all phase changes, for both the transmitted and
reflected rays, occurring at the air-SiO and SiO-Si interfaces.
(ii) For the SiO coated Si solar cell, calculate the minimum film thickness required to
minimize reflection losses of solar radiation of wavelength
λ = 550 nm. (Refractive
indices: Silicon cell:
n Si
= 3.5; Coating,
n SiO
= 1.45) (4 marks)
SiO coating
n=1.
Si
n=3.
air
n=1.
Question 5 (Marks 10)
A student attends a physics lecture with a camera to record the notes the lecturer has projected on to
the theatre’s screen. The camera has a lens diameter of 2mm. The lecturer has written the notes in
blue ink (
λ blue
= 450 nm) and each character (letter or symbol) can be considered to be a 3mm
diameter circle on the screen.
(i) Will the camera resolve individual characters on the screen if the student sits at the back of
the theatre, at a distance of 25 m from the screen? If not,
(ii) what is the minimum distance the camera must be from the screen such that individual
characters are just resolvable?
Note: a plain yes/no answer will obtain no marks; the principle and argument used to show
resolvability must be given, with a simple sketch if appropriate, along with all working in your
calculation.
Question 7 (Marks 11)
(a) Calculate the de Broglie wavelength of a 25 kV electron. You may ignore relativistic effects.
(b) The lifetime of the unstable hydrogen
n = 2 state is approximately 10 ns. Using Heisenberg's
Uncertainty Principle determine the number of significant figures that may be used to express
its energy.
(c) Provide a simple labelled sketch showing the fundamental difference between a direct and an
indirect gap semiconductor. Name one semiconductor material of each type.
