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Students - AS level (16-19)

As well as browsing the rest of the site looking at imaging techniques you can test your knowledge of relevant AS Physics.

1. (a) In a nuclear reactor, a uranium nucleus absorbs a neutron to form a new isotope of uranium. ( U 238/92)
(i) Write down a nuclear equation for this absorption process. [2 marks]

(ii) The new isotope of Uranium decays by b-emission to an isotope of neptunium (Np). Write down a nuclear equation for this decay. [2 marks]

(b) It is suggested that some radioactive waste could be stored underground in simple metal containers and would not cause damage to the enviroment. Comment on this suggestion. [4 marks]

(Marks available: 7)

Source: OCR 2000 Answer
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2. The Joint European Torus (JET) fusion experiment involves the confinement of plasma.
(a) Explain what is meant by plasma. [2 marks]

(b) State the method by which the plasma in the JET experiment is confined.[2 marks]

(c) State two possible advantages of using nuclear fusion reactors as an energy source.

1.
2.

(d)(i) Calculate the electric potential energy of the two hydrogen nucleii when their separation is 2.6 x 10exp-15 m.

energy =
[1 mark]

(iii) For fusion of two hydrogen nucleii to take place, the separation of the nuclei must be less than 2.6 x 10exp-15m. Given that the kinetic energy Ek of a hydrogen nucleus is related to the thermodynamic temperature T by the expression Ek = 2.07 x 10exp-23 T, estimate a minimum value for the temperature of hydrogen for fusion of its nucleii to be possible.

temperature =
[2 marks]

(iii) The temperature of the interior of the Sun is of the order of 10exp7K. Comment on this statement in relation to your answer in (ii) [2 marks]

(Marks available: 9)

Source: OCR 2000 Answer
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3. Read the following passage, and answer the questions which follow.
In the synchrotron, a pulse of particles is made to follow a circular path many times within an evacuated tube. A special device, called a cavity, is arranged on the circle and provides an alternating electric field which accelerates the particles. The oscillations of electric field are synchronised so that each time the pulse of particles crosses the cavity, it gains energy. The pulse of particles is held in a circular path during this process by powerful electromagnets placed around the path, as illustrated in fig.4.1 The strength of the magnetic field is continually increased during the process of acceleration.

(a) State why the synchrotron tube is evacuated. [1 mark]

(b) The particles in this accelerator are protons and the path is clockwise, as illustrated in Fig 4.1. On Fig 4.1, draw an arrow labelled E to show the direction of the electric field in the cavity as the protons pass through it. [2 marks]

(c) Explain why it is necessary to increase the magnetic field strength during the accleration of a pulse of particles. [2 marks]

(d) State two differences between the principles of operation of a synchrotron and those of a cyclotron

1.
2.
[4 marks]

(Marks available: 9)

Source: OCR 2000 Answer
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4. (a) Explain the terms
(i) antiparticle,
[2 marks]

(ii) annihilation
[2 marks]

(b) A positron and an electron annihilate in a collision when the particles are moving in opposite directions at the same low speed.
Calcuate

(i) the total energy in eV involved in the annihilation process,

energy = ................eV
[3 marks]

(ii) the frequency of one of the photons produced.

frequency = Hz
[2 marks]

(Marks available: 9)

Source: OCR 2000 Answer
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5. 18 kV accelerating voltage is applied across an X-ray tube. Calculate:
the velocity of the fastest electron striking the target,
the minimum wavelength in the continuous spectrum of X-rays produced.
(Mass of electron = 9 x 10exp-31 kg;
Charge on electron = 1.6 x 10exp-19 C;
h = 6.6 x 10-34 Js, c = 3 x 10exp8 m/s)

[ 8 x 10exp7 m/s; 6.9 x 10exp-11 m ] Solution

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6. An X-ray tube is operated with an anode potential of 10 kV and an anode current of 15 mA. Calculate
the number of electrons hitting the anode per second,
the rate of production of heat at the anode stating any assumptions made and
the frequency of the emitted X-ray photon of maximum energy.
e = 1.6 x 10exp-19 C h = 6.6 x 10exp-34 Js

[ 9.4 x 10exp16 /s; 150W; 2.4 x 10exp18Hz ] Solution