AQA A Level Physics Paper 3 Section B: Turning points in physics November 2021 question paper 7408/3BD

Figure 1 shows the apparatus used in an experiment to investigate electron diffraction and the de Broglie hypothesis.

Explain how high-speed electrons are produced in the apparatus in Figure 1.

In your answer you should:

• name parts A and B

• discuss the purposes of potential differences V₁ and V₂.

In the experiment, electrons are incident on a target made of a crystalline material. The electron wavelengths need to be about 50% the size of an atom to produce a diffraction pattern on the screen.

Suggest a suitable value for V₂. Support your answer with a calculation.

Figure 2 shows a typical diffraction pattern produced on the screen by the electrons.

Explain how measurements made with the apparatus in Figure 1 can be used to support the de Broglie hypothesis.

STM and TEM are abbreviations for two types of electron microscope.

Which row links the type of microscope to a relevant property of moving electrons?

In 1864, James Clerk Maxwell published a theory that included an equation for the speed of electromagnetic waves in a vacuum.

Show that Maxwell’s theory agrees with the accepted value for the speed of light in a vacuum. Use information from the Data and Formulae Booklet in your answer.

Between 1886 and 1889, Heinrich Hertz completed a series of experiments in an attempt to verify Maxwell’s theory. Figure 3 shows a simplified arrangement similar to the one used by Hertz in one of his experiments.

T is a radio wave transmitter with an aerial consisting of two vertical metal rods. D is a detector that uses a conducting loop aerial.

T is switched on so that an oscillating current is produced in the metal rods. An emf is detected in the conducting loop aerial.

Explain this experiment with reference to Maxwell’s model of electromagnetic waves.

In a different experiment Hertz used stationary waves to determine the speed of radio waves. Figure 4 shows an experimental arrangement similar to the arrangement Hertz used.

Stationary waves are produced between the fixed transmitter and the fixed metal reflector.

In one experiment the distance between the transmitter and reflector is about 12 m and the transmitter frequency is 75 MHz.

Deduce whether this arrangement can be used to measure the speed of electromagnetic waves suggested by Maxwell’s equation.

Figure 5 shows the features of a Michelson-Morley interferometer.

Explain how, using this arrangement, Michelson and Morley attempted to detect the absolute motion of the Earth.

In your answer you should:

• outline the experimental procedure

• explain the expected result of the experiment

• describe the actual result and explain the significance of this result.

State what is meant by an inertial frame of reference.

A pair of detectors is set up to measure the intensity of a parallel beam of unstable particles. In the reference frame of the laboratory, the detectors are separated by a distance of 45 m. The speed of the particles in the beam is 0.97 c.

The intensity of the beam at the second detector is 12.5% of the intensity at the first detector.

Calculate the half-life of the particles in the reference frame in which they are at rest.

In calculations involving time dilation, it is important to identify proper time.

Identify the proper time in the calculation in Question 04.2.