VCE Physics External Assessment Practice Questions – Short Answer

Question 6

Calculate the altitude of the satellite after its descent. (2 marks)

Hint: Use a similar approach to question 5. Make sure to calculate altitude, and not orbital radius.

Question 7

Two protons repel from each other at a distance of 3.3 x 10^-7 m. Each proton has a mass of 1.67 x 10^-27 kg. What is the magnitude of the electric force between the two protons? (2 marks)

Question 8

Suppose that a 5m wire is placed in a uniform magnetic field of 0.15 T, and the maximum force on this wire is 2 N. What must the current in this wire be? (2 marks)

Hint: Rearrange the equation first, then substitute values.

Question 9

Is the Earth’s magnetic field stronger at the poles or the equator? Justify your answer. (2 marks)

Hint: Use two to three lines. The first should state the answer, and the rest should explain that answer based on what you have learnt. Try drawing Earth’s magnetic fields.

Question 10

An electron (charge -e) and a positron (charge +e) approach each other. They are currently at a distance of r. If this distance halves, by what factor does the electric force between them change. (2 marks)

Hint: Try to use a proportional symbol in the electric force equation. What is constant and what changes?

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Question 11

Briefly explain the purpose of a commutator in an electric motor. (2 marks)

Hint: What would happen if the commutator was not there? Think about the forces on the loop.

Question 12

The following information relates to questions 12 & 13.

An electron is accelerated from rest through a field of 5.0 kV. Assume that the electron has a mass of 9.11 x 10^-31 kg.

What is the speed of the electron after acceleration (ignoring relativistic effects)? Give your answer in m/s². (2 marks)

Hint: How much energy does the electron have after acceleration? Can you convert this into SI?

Question 13

When it exits the gun, the electron passes into a magnetic field of strength 10.0 mT, perpendicular to the electron’s motion. What is the radius of the electron beam? Give your answer in mm. (3 marks) 

Hint: If you don’t have the equation in your notes, try deriving it from circular motion and the magnetic force on the electron.

Question 14

An electron beam is generated using a similar method to the one above. If the radius of the electron’s orbit is 32.1 mm, the magnetic field strength is 13 mT, and the velocity of the electron is 7.33 x 10⁷ m/s. Show that the mass of the electron is 9.11 x 10^-31 kg. (2 marks)

Hint: Rearrange the equations you used above for mass, and then make sure to finish the question by stating what you have shown.

Question 15

The image above shows an electron in a constant magnetic field, and its initial velocity. Draw the path of the electron as it moves through this field. (1 mark)

Hint: Make sure to consider the direction of positive charge. The drawing should clearly show both the path and the direction of the electron around this path.

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Question 16

A rectangular coil with an area of 20 cm² and a resistance of 4.0 Ω is placed in a uniform magnetic field with strength 6.0 mT. What is the magnitude of the EMF generated when the magnetic field is doubled in 50 ms? (2 marks)

Hint: Make sure to convert the units into SI.

The following information relates to questions 17-20.

Suppose that a 10 km power line (resistance 3 Ω/km) is used to transfer power from a wind turbine to a city. At the generator, 240 V is stepped up using a coil ratio of N2/N1 = 50. Assume that the turbine outputs 2.75 MW.

Question 17

What is the current in the power line? (3 marks)

Hint: Make sure to correctly apply the transformer equations.

Question 18

How much power is lost in the power line? (1 mark)

Question 19

The transformer at the city steps down the voltage back to 240V. What current is delivered to the city? (2 marks)

Hint: The percentage of current lost is equal to the percentage of power lost. Why?

Question 20

How can the power lost realistically and efficiently be reduced? (1 mark)

Hint: Think about the cost/ ease of your solution.

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Question 21

A Golfer hits a ball from a tee 4cm above the ground, with an initial velocity of 24 m/s at an angle of 52°. If the ball hits the green, which is 1.2 m above the ground, how far has it travelled? (3 marks)

Hint: Make sure to draw the trajectory of the ball. What do you know about the vertical and horizontal motion of the ball?

Question 22

A shuttle travels between two systems at a constant velocity of 3.2 x 10⁸ m/s. A stopwatch on the satellite measures the length of this journey as 4 Years. What time would an observer floating at rest in space measure? (2 marks)

Hint: Will the answer be shorter or longer than 45s?

Question 23

Briefly explain how Hyugen’s principle implies that light waves curve towards the normal as they enter water from air. (2 marks)

Hint: Consider the speed of light in these two substances.

Question 24

How does the wave model of light fail to explain the result of Einstein’s photoelectric experiment? (2 marks)

Hint: Your answer should reference the different results for varying frequency and amplitude in this experiment.

Question 25

Assume that a volleyball (mass 270g) is travelling at a speed of 2.1 m/s. What is the de Broglie wavelength of this volleyball? (2 marks)

Hint: Make sure to convert the units first.

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