AQA A Level Physics Paper 3 Section B: Turning points in physics June 2017 question paper 7408/3BD

When a large potential difference is applied between the cathode and anode the paddle wheel is seen to rotate and travel along the rail towards the anode.

Explain how this experiment led Crookes to conclude that cathode rays are particles and that these particles caused the movement of the paddle.

Later experiments showed that cathode rays are electrons in motion.

Explain how cathode rays are produced in a gas discharge tube.

In a particular gas discharge tube, air molecules inside the tube are absorbed by the walls of the tube.

Suggest the effect that this absorption may have on the motion of the paddle wheel.

Give a reason for your answer.

The following observations are made.

A When the speed of rotation is low the observer sees the light returning after reflection by the mirror M.

B When the speed of the wheel is slowly increased the observer continues to see the light until the wheel reaches a certain speed. At this speed the observer cannot see the light.

Explain these observations.

Observation A

Observation B

Table 1 shows data from Fizeau’s experiment at the instant when observation B is made.

It can be shown that the speed of light c is given by the equation

c = 4 dnf

Discuss whether the data in Table 1 are consistent with the present accepted value for the speed of light.

The speed of the wheel is further increased.

Deduce the value of f when the observer would next be unable to see light returning from the mirror.

Explain how the nature of light is implied by Maxwell’s theory of electromagnetic waves and Fizeau’s result.

What is the process by which electrons are produced in an electron gun? Tick () the correct box.

The electrons in a particular TEM have a kinetic energy of 4.1 × 10^–16 J. Relativistic effects are negligible for this electron energy.

Suggest, with a calculation, whether the images of individual atoms can, in principle, be resolved in this TEM.

A typical TEM can accelerate electrons to very high speeds and form high resolution images.

Explain:

the process of image formation, and

the factors that affect the quality of, and the level of detail in, the image.

A student models a spacecraft journey that takes one year. The spacecraft travels directly away from an observer at a speed of 1.2 × 10⁷ m s⁻¹. The student predicts that a clock stationary relative to the observer will record a time several days longer than an identical clock on the spacecraft.

Comment on the student’s prediction. Support your answer with a time dilation calculation.

In practice, the gravitational field of the Sun affects the motion of the spacecraft and it does not travel directly away from the Earth throughout the journey.

Explain why this means that the theory of special relativity cannot be applied to the journey.

Calculate the velocity of the protons as a fraction of the speed of light.