L.35
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PRE-LEAVING CERTIFICATE EXAMINATION, 2014
PHYSICS – ORDINARY LEVEL
TIME – 3 HOURS
Answer three questions from Section A and five questions from Section B.
N.B. Relevant data are listed in the Formulae and Tables booklet, which is available
from the Superintendent.
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SECTION A (120 marks)
Answer three questions from this section. Each question carries 40 marks.
1. A student performed an experiment to investigate the laws of equilibrium for a set of
co-planar forces. The student found that the centre of gravity of the metre stick was at the 50 cm mark and measured its weight. The student then applied a set of forces to the metre stick, as shown in the diagram below.
4.0 N 6.0 N
5.0 N 4.0 N
100 20 30 40 50 60 70 8 0 90 100
(i) How did the student find the centre of gravity of the metre stick? (6) (ii) How did the student measure the weight of the metre stick? (3) (iii) How did the student apply the upward and downward forces to the metre stick? (6) (iv) By finding the total upward and downward forces and using one of the laws of
equilibrium, calculate the weight of the metre stick that the student would have measured. (11)
(v) Calculate (a) the sum of the clockwise moments about the 50 cm mark and
(b) the sum of the anticlockwise moments about the 50 cm mark. (11) (vi) Explain how the student’s calculations verify the second law of equilibrium. (3) 2. In an experiment to measure the specific heat capacity of a substance, a number of
temperature and mass measurements were recorded. Some of these measurements were made before the substance was heated and some were made after heating. The specific heat capacity was then calculated based on these measurements.
(i) Draw a labelled diagram of the apparatus used in the experiment. (12) (ii) State two measurements of mass that were taken during the experiment. (6) (iii) State two temperature readings that were taken during the experiment. (6) (iv) Explain, using relevant formulae, how the specific heat capacity of the substance was
calculated using these values. (10) (v) State two precautions that could have been taken to ensure a more accurate result. (6)
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3. In an experiment to measure the wavelength of a monochromatic light source using a diffraction grating, angular measurements were taken on either side of the central fringe. The spacing between each line in the grating was 2 × 10–6 m. The average of the two second order (n = 2) fringe angle readings was found to be 24.2.
(i) What is monochromatic light? (3) (ii) Draw a labelled diagram of the apparatus used in the experiment. (12) (iii) Explain how the angle was measured for both second order fringes. (9) (iv) Calculate the wavelength of the monochromatic light using the data. (12) (v) Give a possible source of error in this experiment. (4) 4. A student investigated the variation of current I with potential difference V for a
semiconductor diode in forward bias. (i) What instruments were used by the student to measure (a) the potential difference
and (b) the current? (6) (ii) Draw a labelled diagram of the circuit used to collect the data in this experiment. (16) The table shows the measurements recorded by the student.
V/V 0 0.2 0.4 0.6 0.8 1.0
I/mA 0 1 2 19 52 111 (iii) Plot a graph on graph paper to show the variation of current I with potential difference V
for the semiconductor diode. (Put V on the X-axis.) (12) (iv) Use the graph to estimate the potential difference when the current is 40 mA. (6)
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SECTION B (280 marks) Answer five questions from this section. Each question carries 56 marks.
5. Answer any eight of the following parts (a), (b), (c), etc. (a) State the principle of conservation of momentum. (b) What is the pressure exerted on the ground by a person of weight 800 N whose feet
have 0.02 m2 in contact with the ground? (c) Give two examples of thermometric properties. (d) How does the frequency vary with length for a stretched string? (e) Which of the following is the unit for capacitance? Weber Tesla Farad Coulomb (f) What is extrinsic conduction in semiconductors? (g) Where must an object be placed so that it forms a
virtual image in a concave mirror? (h) Name two factors that determine the size of the force on a
current-carrying conductor in a magnetic field. (i) State two applications of X-rays. (j) Name the scientist who measured the amount of charge on an electron.
(8 × 7)
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6. State Newton’s first and second laws of motion. (12) A car of mass 1200 kg is travelling down a hill and the driver takes his foot off the
accelerator. The car continues to travel at a constant speed of 30 m s–1. (i) Draw a diagram showing two of the forces acting on the car after the driver has taken
his foot off the accelerator. (9) While still travelling at a speed of 30 m s–1, the road becomes level. (ii) If the driver keeps his foot off the accelerator and the brake, why would you expect the
car will come to a stop? (6) The car passes an electricity pole at the point where the road levels. (iii) If the electricity poles are 40 m apart and it takes 15 seconds for the car to stop, what
distance will it take the car to stop from the first electricity pole? How many electricity poles will it pass during this time? (15)
(iv) Calculate the size of the force that stops the car. (6) (v) Describe two situations where the force that stops the car could be reduced. (8)
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7. (a) Polaroid glasses use the principle of polarisation of light. (i) Explain the underlined term. (6) (ii) If you have two pieces of polaroid material, how
would you use them to demonstrate polarisation? (8) (iii) Why is polarisation not observed for sound waves? (6) (b) (i) Microwaves are electromagnetic waves. Name two types of radiation in the
electromagnetic spectrum that have higher frequencies than microwaves. (6) A speed gun transmits microwaves that have a frequency of 10 GHz. A car moves
towards a Garda officer holding a speed gun at a constant speed of 40 m s–1. When the Garda first observes the car, it is 400 m away from him.
(ii) How long will it take for the transmitted wave to reflect off the car and return to
the speed gun? (8) (iii) Sometime later the speed gun detects a frequency of 9 GHz. What can you conclude about the motion of the car in relation to the Garda at this
time? Explain your answer. What is the name given to the effect that causes this change in frequency? (12) (iv) The effect referred to in (iii) also allows us to determine whether stars are moving
away from or towards the Earth. If red shift is observed, what does that tell us about the motion of the star relative to the Earth? (4)
(v) Why can changes in frequency of sound, but not light, be observed for everyday
events on the surface of the earth? (6)
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8. A periscope uses total internal reflection in two prisms to redirect light as shown in the diagram. The prism must be made of a material whose critical angle is greater than 45.
(i) Define the underlined terms. (12) (ii) Why is the light ray in the diagram not refracted
when it strikes the first surface of the prism? (6) (iii) Calculate the minimum refractive index that
will allow total internal reflection in each prism. (9) (iv) Draw a ray diagram to show how you could construct
a periscope using two mirrors instead of two prisms. (9) (v) The person looking at the periscope is long-sighted.
Why does this not matter when using the periscope? Describe, using a diagram, how this person corrects for long-sightedness. (15)
(vi) Give one other application of total internal reflection. (5) 9. An electrical generator is based on the principle of electromagnetic induction. A generator
can be as small as the simple dynamo that powers the light on a bicycle or large as a turbine in a generating station, powering thousands of houses.
(i) What is electromagnetic induction? (6) (ii) State the energy conversion that takes place in an electrical generator. (6) (iii) State Faraday’s law of electromagnetic induction and describe an experiment that
demonstrates Faraday’s law. (18) (iv) Alternating current (a.c.) is produced by an electrical generator. Explain the underlined
term. Sketch a graph to show how a.c. voltage varies with time. (9) (v) Why is a.c. electricity transmitted over long distances at high voltage? (6) (vi) Name the device used to convert very high voltages to 230 V before electricity enters
homes in Ireland. This device is used to convert 10000 V to 230 V before entering a house.
If there are 200 turns in the secondary coil of the device, how many turns are in the primary coil? (11)
Periscope
Eye
Light ray
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10. Radioactivity was discovered by Henri Becquerel in 1896 and many more discoveries about radioactivity were made by Marie and Pierre Curie in the following years. These three scientists jointly received the Nobel Prize for Physics in 1903.
(i) What is radioactivity? (6) (ii) Alpha ()-particles, beta ()-particles and gamma ()-rays are the three types of
radiation produced in radioactivity. What are -particles, -particles and -rays? (9) (iii) List the three forms of radiation in increasing order of penetrating power. Describe an experiment that compares the penetrating power of -particles, -particles
and -rays. (15) (iv) U23892 emits an -particle. The new nucleus formed then emits a -particle. Using page 82 of the Formulae and Tables booklet, name the element that is formed
after each of these radioactive nuclei decays. (12) (v) The unit for the rate at which radioactivity occurs is named after one of the three
scientists that won the Nobel prize in 1903. Name the scientist and define the unit. (9) (vi) State one use of radioisotopes. (5)
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11. Read this passage and answer the questions below. The sun is the star at the centre of the solar system.
Chemically, about three quarters of the sun’s mass consists of hydrogen, while the rest is mostly helium. The remainder (1.69%, which nonetheless equals 5,628 times the mass of the earth) consists of heavier elements, including oxygen, carbon, neon and iron.
The sun formed about 4.6 billion years ago from the
gravitational collapse of a region within a large molecular cloud. Most of the matter gathered in the centre, while the rest flattened into an orbiting disk that would become the solar system. The central mass became increasingly hot and dense, eventually
initiating thermonuclear fusion in its core. It is thought that almost all other stars form by this process. The surface temperature of the sun is approximately 5778 K. The sun, like most stars, is a main-sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the sun fuses 620 million metric tons of hydrogen each second.
(Adapted from Wikipedia.)
(a) What is the temperature of the surface of the sun in C? (b) What is the form of heat transfer by which heat travels from the sun to the earth? (c) Why are the other two forms of heat transfer not involved in transferring heat from the
sun to the earth? (d) Solar energy can be transferred to other forms of energy on the surface of the Earth.
Give two examples of where this occurs. (e) What is nuclear fusion? (f) Why is there more helium in the sun now than several billion years ago? (g) What caused the sun to be formed 4.6 billion years ago? (h) Why are nuclear fusion reactors better for the environment than nuclear fission reactors?
(8 × 7)
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12. Answer any two of the following parts (a), (b), (c), (d). (a) State the principle of conservation of energy. (6) A girl bounces a basketball of mass 600 g into the ground. After the first bounce, it
starts rising at 5 m s–1. She leaves it to bounce a number of times. Calculate (i) The kinetic energy of the basketball as
it leaves the ground after the first bounce. (6) (ii) The height reached by the basketball
after the first bounce. (7) The basketball reaches a height of 1 m after the second bounce. (iii) How much energy is lost during the second bounce? (6) (iv) State one way the energy could have been lost. (3) (acceleration due to gravity, g = 9.8 m s–2) (b) In many workplaces warning signs are displayed for workers
to wear ear protection when the sound intensity is above a certain value.
In a sound level meter, an adapted version of the scale
using the unit of sound intensity level is used. (i) What is the name of the scale used in the sound
level meter? (3) (ii) Why is this scale used? (6) (iii) What is meant by the threshold of hearing
of the ear? (6) (iv) Some devices produce sound that is audible to young people but often cannot be
heard by older people. Explain why this may happen. (7) (v) Give two examples of situations where ear protection would need to be worn
continuously. (6)
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(c) If two charges are near each other, they exert a force on each other as described by Coulomb’s law.
(i) State Coulomb’s law. (9) (ii) Copy this pair of positive charges into your answerbook and draw the electric
field pattern that exists around them. (6)
+ +
(iii) The potential difference between two points in an electric field is 20 V.
If it takes 60 J of work to move a positively-charged object between those two points, what is the size of the charge on the object? (7)
(iv) State one use and one hazard of electric fields. (6) (d) The diagram shows a cathode ray tube.
A
B C
(i) What is emitted from A? Explain the process by which it is emitted. (12) (ii) What is not shown in the diagram between A and B? Why does this need to be
present between A and B? (9) Cathode rays are deflected by the plates at C. (iii) By drawing the plates at C, show what charge could have been placed on the
plates to achieve the deflection shown in the diagram. (7)
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