PHYSICS — HIGHER LEVEL -...

_______________

PRE-LEAVING CERTIFICATE EXAMINATION, 2010

_______________

PHYSICS — HIGHER LEVEL

_______________

TIME: 3 HOURS_______________

Answer three questions from section A and fi ve questions from section B.

of 9

of 9

SECTION A (120 marks)

Answer three questions from this section.Each question carries 40 marks.

____________________________

1. A 2.0 kg object moving with a velocity of 8.0 ms–1, collides with a 4.0 kg object moving with a velocity of 5.0 ms–1 along the same line. If the two objects join together on impact, calculate their common velocity when they are initially

(i) in the same direction

(ii) in opposite directions. (12)

Describe the apparatus which might have been used to do this experiment in the laboratory. (9) What would be used to ensure the two objects join together on impact? (6)

What readings needed to be taken in order to calculate the velocity? (6)

Why does this experiment need to be carried out within a closed system? (7)

2. A student passed a ray of light through a rectangular glass block from air. He measured the angles of incidence for fi ve rays of light entering the glass block and the corresponding angles of refraction. The following results were obtained:

i/degrees 30° 40° 50° 60° 70°r/degrees 20° 25°30` 32° 35° 39°

Draw a suitable graph and explain how this verifi es Snell’s law. (15)

From the graph determine the refractive index of the glass. (9)

Which value of r would be the least accurate result? Explain. (6)

Describe another experiment to determine the refractive index of the glass block. (Include the formula used.) (10)

of 9

3. In a experiment to investigate the variation of the fundamental frequency of a string with its length, the following results were obtained:

l/cm 20 30 40 50 60 70 80 90 100f/Hz 675 455 335 273 230 193 173 150 134

How would the student have known that the string was vibrating at its fundamental frequency? (6)

Draw a suitable graph to illustrate the relationship between the fundamental frequency and the length of the stretched string. State this relationship. (15)

Determine from the graph the ratio of the tension to the mass per unit length. (12)

Explain how the temperature would affect this value. (7)

4. The electrical resistance per metre of nichrome wire was measured at different diameters. The results are as follows:

Diameter/mm 0.815 0.458 0.28 0.188 0.158 0.118Resistance/Ωm–1 2.04 6.44 17.32 38.2 54.52 99

Name the apparatus used to measure the diameter of wire. Why is it advisable to measure the diameter of any wire more than once? (6)

Assuming that each piece of wire is of circular cross-section, calculate the cross-sectional area A of each wire. (9)

Draw a suitable graph to illustrate the relationship between R and A. (15)

Use your graph to estimate the resistivity of the alloy nichrome. (10)

________________________________________________________________________________

of 9

SECTION B (280 marks)

Answer fi ve questions from this section.Each question carries 56 marks.

____________________________

5. Answer any eight of the following parts (a), (b), (c) etc.

(a) When would an object moving at constant speed have an acceleration? (7)

(b) If the potential energy of a body is 980J at a height of 2 m, what is the weight of the body? (7)

(c) The critical angle for water is 48.6°. Find its refractive index. (7)

(d) A diffraction grating has 500 lines per mm. What is the distance in metres between adjacent lines? (7)

(e) Give a use of capacitors. (7)

(f) State Lenz’ law. (7)

(g) Who discovered radioactivity in 1890? (7)

(h) What initiates the fi ssion of a uranium nucleus? (7)

(i) Name two factors on which the back emf of a motor depends? (7)

(j) Distinguish between baryons and leptons.

or

State the principle of moving coil meters. (7)

of 9

6. Distinguish between a scalar quantity and a vector quantity. (6)

Describe an experiment to fi nd the resultant of two vectors. (18)

Defi ne acceleration. (6)

A body is travelling with a velocity u in a certain direction. It then accelerates uniformly in the same direction for a time t. Derive an expression for its displacement after time t in terms of u and a. (11)

A car accelerates uniformly from rest to a speed of 15ms–1 in a time of 4 seconds. It then moves at a constant speed for the next 6 seconds.

Calculate:

(i) The total distance travelled by the car.

(ii) The average speed of the car over the whole journey. (15)

7. Explain the term resonance. Give an example of resonance. (9)

A tuning fork is set vibrating over a resonance tube which can be varied from 0 cm to 110 cm in length. At what lengths would you expect to fi nd resonance if the tuning fork has a frequency of 425Hz and the speed of sound is 340ms–1. (12)

In the laboratory, the vibrating tuning fork is held slightly above the resonance tube. How is this error in the measurement of length overcome? (6)

A police car siren emits a continuous note of frequency 1 kHz as it passes a stationary observer at the traffi c lights. If the police car travels at 30ms–1 towards the observer, the frequency of the note appears to be higher. Explain with the aid of a diagram, why the frequency of the note appears higher to the observer. Name this phenomen. (14)

If the velocity of sound is 336ms–1 on this particular day, what is the frequency heard by the observer when the car is:

(i) approaching the observer;

(ii) moving away from the observer? Give another application of this phenomen. (15)

of 9

8. Explain the term radioactive decay. (6)

Radon-222 is an α-emitter. Write an equation to show the decay of radon-222. (6)

Why is Radon considered to be a health hazard? (5)

In an experiment to determine the half-life of a short-lived radioactive isotope a measure of the activity, A, for a sample of the isotope was obtained at various times t. The following results were recorded.

t/s 0 20 40 60 80 100 120 140 160A/Bq 60 45 35 26 20 17 13 10 7

Draw a suitable graph on graph paper to illustrate the change in activity with time and, from the graph determine the half-life of the isotope. (21)

Describe the apparatus which might have been used in this experiment. What reading should be recorded before the radioactive isotope is released? (12)

Give two safety precautions which should be observed when handling radioactive materials. (6)

9. Defi ne (i) resistance (ii) capacitance. (12)

Two resistors are connected in parallel in a circuit. Show that the effective resistance of the circuit is: R1R2 R1+R2 (9)

Outline an experiment to show that a capacitor stores energy. (12)

Fig. 1 shows a capacitor connected in series to a power supply and a lamp.

Fig. 1

(i) Explain why the bulb does not light. (6)

(ii) Suggest a change to the circuit that would light the bulb. Explain your choice. (8)

(iii) What is the charge on the plates when the energy stored is 0.52 mJ? (9)

1.5 V

4.7 μF

of 9

10. Answer either part (a) or part (b).

(a) Under the guidance of Rutherford, in 1932 Cockcroft and Walton carried out their famous experiment. (i) Write a nuclear equation for this experiment. (9)

(ii) Explain the signifi cance of this experiment. (5)

What is meant by conservation of momentum in nuclear reactions? (6)

Thorium-228 emits an α-particle with a velocity of 4 107ms–1 Write an equation for the reaction. (9)

Calculate the recoil velocity of the resulting nucleus. (15)

Calculate the energy released in the following nuclear reaction.

1 H + 3 Li → 2 He + 2 He + energy (12)

Mass of deuteron = 2.014102 a.m.u. Mass of lithium nucleus = 6.015125 a.m.u. Mass of alpha particle = 4.002604 a.m.u. 1 a.m.u. = 1.66 10–27 kg.

or

(b) What is the function of an induction coil? State the principle on which it is based. Give one application of the induction coil. (12)

Name the Irish physicist who invented the induction coil. (3)

A transformer and an induction coil can both be used to change the size of a voltage. What is the basic difference in the operation of these two devices? (6)

Give two factors that affect the effi ciency of a transformer. (6)

Consider a transformer with a primary coil of 4600 turns and a secondary coil of 240 turns. The input voltage is 230V. Calculate:

(i) the output voltage;

(ii) the output power for a current of 2.4 A;

(iii) the effi ciency if the input power is 29.9 W. (12)

The a.c. generator is similar to a motor in reverse. Explain this statement. (6)

Draw a labelled diagram of the a.c. generator (alternator). (11)

2 46 4

of 9

11. Galileo, mainly remembered in connection with falling objects and pendulums, is attributed with the invention of the thermometer in 1592. The fi rst temperature scale was devised about 100 years later. All early thermometers had one major defect – they did not have a common scale; it was left to the user to interpret the markings!

(‘‘Physics Today’’ by Randal Henly, pg. 141)

(i) Distinguish between heat and temperature. (7)

(ii) Give the equation that defi nes temperature on the Celsius scale. (7)

(iii) What is needed to establish a temperature scale? (7)

(iv) Defi ne specifi c heat capacity. (7)

(v) Why are storage heaters surrounded by bricks of high specifi c heat capacity? (7)

(vi) Name the three methods of heat transfer. (7)

(vii) Explain how a heat pump works. What is the principle on which it works? (7)

(viii) Give a practical application of a heat pump. (7)

of 9

12. Answer any two of the following parts (a), (b), (c), (d).

(a) Defi ne pressure. (6) Deep-sea divers can sometimes develop a condition called “the bends” if they rise back too quickly to the surface of water. Explain briefl y how this condition can arise. (6) The height of mercury in a mercury barometer was 78 cm on a certain day. Given that the density of mercury is 1.36 104 kg m–3 and g = 9.8 m s–2, what was the atmospheric pressure on that day? (7) What is a hydrometer and explain how it works. (9)

(b) Dispersion and total internal refl ection are two phenomena which might occur when light is passed into a prism. Defi ne the underlined terms. (12) Prisms are used in binoculars to refl ect light through an angle of 90°. Illustrate how this occurs. (6) Calculate the minimum value of the refractive index of the material of the prism for this to occur. (10)

(c) What is the photoelectric effect? (6) Write down an expression for Einstein’s photoelectric law. (9) What are X-rays? Who discovered them? (9) Give one reason, why X-rays are considered to be the converse of the photoelectric effect. (4)

(d) State one law of electromagnetic induction. (6) Defi ne magnetic fl ux, Ø. (6)

When a small metal cylinder is dropped through one end of the copper tube as shown in Fig. 2, it falls freely under gravity. If the small cylinder is fi rst magnetised, it then takes much longer to fall through the tube. Explain. (6)

A fl at circular coil of radius 0.8 cm and consisting of 40 turns of wire lies in a plane which is perpendicular to a magnetic fi eld of magnetic fl ux density .20 T. Calculate the magnitude of the induced e.m.f. when the fl ux density is steadily reduced to zero in 0.50 s. (10)

Small metal cylinder

Copper tube

Fig. 2

PHYSICS — HIGHER LEVEL -...

Documents

Transcript of PHYSICS — HIGHER LEVEL -...