OCR A Level Physics A Exploring Physics June 2019 question paper H556/02

Which law indicates that charge is conserved?

A Lenz’s law

B Coulomb’s law

C Kirchhoff’s first law

D Faraday’s law of electromagnetic induction

Your answer

The diagram below shows two uniformly charged spheres separated by a large distance z.

The radius of the small sphere is x and the radius of the large sphere is y.

Which is the correct distance to use when determining the electric force between the charged spheres?

A z

B x + z

C y + z

D x + y + z

Your answer

Coherent radio waves from transmitters X and Y are emitted in phase. The waves interfere constructively at point Z.

The distance XZ is 16.0 m and the distance YZ is 20.0 m. The radio waves have wavelength .

Which value of is not possible?

A 1.0 m

B 2.0 m

C 3.0 m

D 4.0 m

Your answer

A potential divider circuit is shown below.

The resistance of the variable resistor is R. The potential difference across the variable resistor is V.

Which graph shows the correct variation with R of V ?

Your answer

Which of the following statements is/are correct about electromagnetic waves?

1 They can be plane polarised. 2 They can be refracted and diffracted. 3 They have the same speed in a vacuum and in glass.

A Only 1

B Only 3

C Only 1 and 2

D 1, 2 and 3

Your answer

The intensity of a beam of X-rays incident on material P is I₀. The beam passes through 0.50 cm of material P and 0.50 cm of material Q.

The absorption (attenuation) coefficients of P and Q are 0.60 cm^–1 and 0.20 cm^–1 respectively. The intensity of the beam after passing through both P and Q is n I₀.

What is the value of n ?

A 0.67

B 0.74

C 0.82

D 0.90

Your answer

A capacitor is discharged through a resistor.

The capacitor is fully charged at time t = 0. The time constant of the circuit is 10 s. The switch is closed at time t = 0. The current in the resistor is I.

Which row is correct?

Your answer

The number of turns on the coils of four ideal iron-cored transformers A, B, C and D are shown in the table below.

Each transformer is connected in turn to an alternating 240 V supply.

Which transformer will give the largest output current?

Your answer

This question is about waves.

The period of a progressive wave can be determined from Fig. 16.1. Add a correct label to

the horizontal axis so that the period can be found.

A progressive wave has wavelength , frequency f and period T.

Show that the speed v of the wave is given by the equation v = f.

Calculate the period T of the light wave.

The rays of light are in phase at the dashed line X.

Use your two answers above to state the phase difference in degrees between the light rays at Y.

Question 16 continues on page 12

Fig. 17.1 shows the variation with distance of the displacement of a stationary wave at time

The period of the wave is T.

On Fig. 17.1, sketch a graph to show the variation of the displacement at time t =

On Fig. 17.1, show the positions of all the nodes. Label each node N.

State Kirchhoff’s second law and the physical quantity that is conserved according to this law.

On Fig. 18.2 draw the straight line of best fit. Determine the gradient of this line.

gradient =........ A^–1 m^–1

Show that the gradient of the line is , where is the resistivity of the material of the wire, A is the area of cross-section of the wire and E is the e.m.f. of the cell.

The e.m.f. E of the cell is 1.5 V. The diameter of the wire is 0.38 mm.

Use your answer to (i) and the equation given in (ii) to determine .

=........ m

Use Fig. 19.2 to show that the p.d. across the 50 resistor is 0.50 V.

Calculate the e.m.f. E of the power supply.

The LED emits blue light of wavelength 4.7 × 10^–7 m.

Estimate the number of blue light photons emitted from the LED per second.

number of photons per second =........ s^–1

The light from the LED is incident on a metal of work function 2.3 eV.

Explain, with the help of a calculation, whether or not photoelectrons will be emitted from the surface of the metal.

Fig. 20 illustrates a device used to determine the relative abundance of charged rubidium ions.

A uniform magnetic field is applied to an evacuated chamber. The direction of the magnetic field is perpendicular to the plane of the paper.

A beam of positive rubidium ions enters the chamber through a hole at H. The ions travel in a semi-circular path in the magnetic field. The ions are detected at point D.

The chemical composition of ancient rocks found on the Earth can be used to estimate the age of the Earth. Nuclei of rubidium-87 (⁸⁷₃₇Rb) decay spontaneously into nuclei of strontium-87 (⁸⁷₃₈Sr). The half-life of rubidium-87 is 49 billion years.

Name the two leptons emitted in the decay of a rubidium-87 nucleus.

The percentage of rubidium left in a sample of an ancient rock is 95%.

Estimate the age of the Earth in billion years.

age =........ billion years

The key on Fig. 21 shows whether a nucleus is stable, emits a beta-plus particle or emits a beta-minus particle to become stable.

For Z = 7, suggest in terms of N why an isotope may emit

a beta-minus particle

a beta-plus particle.

Inside a nuclear reactor, fission reactions are controlled and chain reactions are prevented. A typical fission reaction of the uranium-235 nucleus (²³⁵₉₂U) is illustrated below.

The neutron triggering the fission reaction moves slowly. The neutrons produced in the fission reaction move fast.

Describe what is meant by chain reaction.

Explain how chain reactions are prevented inside a nuclear reactor.

The energy released in each fission reaction is equivalent to a decrease in mass of 0.19 u. A fuel rod in a nuclear reactor contains 3.0% of uranium-235 by mass.

Estimate the total energy produced from 1.0 kg of fuel rod.

molar mass of uranium-235 = 0.235 kg mol^–1 1 u = 1.66 × 10^–27 kg

Use Fig. 22.2 to propose and carry out a test to show that Q is inversely proportional to d.

Test proposed:

Working:

Use capacitor equations to show that Q is inversely proportional to d.

* Fig. 22.4 shows an arrangement used by a student to investigate the forces experienced by a small length of charged gold foil placed in a uniform electric field.

The two vertical metal plates are connected to a high-voltage supply.

The foil is given a positive charge by briefly touching it to the positive plate.

The angle made with the vertical by the foil in the electric field is given by the expression

where q is the charge on the foil, E is the electric field strength between the plates and W the weight of the foil.

The angle can be determined by taking photographs with the camera of a mobile phone.

Describe how the student can safely conduct an experiment to investigate the relationship between and E.

Identify any variables that must be controlled.

Additional answer space if required.

Describe the basic structure of an X-ray tube and explain how X-ray photons are produced. You may draw a labelled diagram.

A beam of X-rays is directed at tissues in a patient. The X-ray photons interact with the atoms of the tissues.

Simple scatter is one of the attenuation mechanisms.

Name and describe two other attenuation mechanisms.

Explain how an ultrasound transducer can emit ultrasound. You do not need to describe the design of the transducer.

Explain how the reflection of ultrasound at a boundary between two tissues depends on the physical properties of the tissues.