OCR A Level Physics A Exploring Physics November 2020 question paper H556/02

The Doppler effect is used to measure the speed of blood flow in arteries.

Which medical diagnostic method uses this technique?

A barium scan

B CAT scan

C PET scan

D ultrasound scan

Your answer

Which sequence shows the materials arranged in the order of increasing number density of charge carriers?

A conductor, insulator, semiconductor

B conductor, semiconductor, insulator

C insulator, semiconductor, conductor

D semiconductor, insulator, conductor

Your answer

Electromagnetic radiation is incident on a metal of work function 2.3 eV. The maximum kinetic energy (KE) of the photoelectrons is 1.7 eV.

The frequency of this incident electromagnetic radiation is kept the same but its intensity is doubled.

What is the maximum KE of the photoelectrons now?

A 1.7 eV

B 2.9 eV

C 3.4 eV

D 4.0 eV

Your answer

A student is doing an experiment on the magnetic force experienced by a current-carrying wire in a uniform magnetic field. The magnetic flux density B can be varied.

For a particular flux density, the current in the wire is 2.0 A. The length of the wire in the field is 0.12 m. The angle between the current and the magnetic field is 30°. The force experienced by the wire is 7.7 × 10⁻² N.

The student calculates B and records the results in a table.

Which row shows the correct table heading for B and the correct value for B ?

Your answer

The diagram below shows the oscilloscope trace for an electrical signal.

The time-base setting of the oscilloscope is 2 s cm⁻¹.

What is the frequency of the signal?

A 125 Hz

B 250 Hz

C 125 kHz

D 250 kHz

Your answer

This question is about a progressive wave and a stationary wave.

Which statement is correct?

A A progressive wave has at least one node.

B All progressive waves are longitudinal.

C All particles oscillating between two adjacent nodes in a stationary wave are in phase.

D The superposition of two waves travelling in the same direction produces a stationary wave.

Your answer

The diagram below shows a circuit used to charge a capacitor.

The power supply has electromotive force (e.m.f.) 10 V and negligible internal resistance. The capacitor has capacitance C and the resistor has resistance R. The switch is closed at time t = 0. The table below shows potential difference V across the resistor at various values of time t.

What is the product C × R for this circuit?

A 0 s

B 2.8 s

C 4.2 s

D 6.0 s

Your answer

A capacitor discharges through a resistor. At time t = 0 the potential difference V across the capacitor is V₀. At time t = 2.0 s, V = 0.90 V₀.

Which statement is not correct?

A At t = 4.0 s, V = 0.81 V₀.

B The capacitor is fully discharged after t = 10 s.

C The potential difference across the resistor is the same as that for the capacitor.

D The potential difference V decreases exponentially with time t.

Your answer

A student is modelling the decay of a radioactive source using the equation N / t = −0.5 N. The student decides to use t = 0.10 s. The number N of radioactive nuclei is 2000 at t = 0.

Part of the modelling spreadsheet from the student is shown below.

What is the value of N at t = 0.30 s?

A 1700

B 1710

C 1715

D 1805

Your answer

The table below shows the quark compositions of four particles A, B, C and D.

Which particle has a positive charge?

Your answer

The potential difference across a lamp is 2.5 V. The current in the lamp is 20 mA.

What is the energy dissipated in the lamp in 3.0 hours?

A 0.050 J

B 0.15 J

C 9.0 J

D 540 J

Your answer

What can be deduced from the diffraction of electrons by a thin film of graphite?

A Electrons are leptons.

B Electrons are negatively charged.

C Electrons interact with atoms on a one-to-one basis.

D Electrons travel as waves.

Your answer

This question is about the medical use of ultrasound.

In ultrasound scanning, explain what is meant by impedance (acoustic) matching and how it may be achieved.

There are several different types of ultrasound scanning techniques.

Explain how an A-scan could be used to measure the thickness of a patient’s eye lens. You may draw a diagram to help with your answer.

A light-emitting diode (LED) emits red light when it is positively biased and has a potential difference (p.d.) greater than about 1.8 V.

The energy of a photon of red light is about 1.8 eV.

Calculate the wavelength of this red light.

The LED is connected into a circuit, as shown below.

The battery has electromotive force (e.m.f.) 4.5 V and negligible internal resistance. The resistor R has resistance 150 . Assume the p.d. across the LED is 1.8 V.

The diagram below shows a circuit designed by a student.

The LED is very close to, and facing the light dependent resistor (LDR). The circuit is taken into a dark room.

The student thought that the LED would switch on. Instead, the LED was found to repeatedly switch on and off.

Explain this behaviour of the LED in this potential divider circuit.

Suggest a possible refinement so that the LED switches on permanently when taken into the dark room.

The Planck constant h is an important fundamental constant in quantum physics.

Determine the S.I. base units for h.

A researcher is investigating the de Broglie wavelength of charged particles.

The charged particles are accelerated through a potential difference V. The de Broglie wavelength of these particles is then determined by the researcher.

Each particle has mass m and charge q.

A sound wave is incident at the ear.

The amplitude of the sound wave is 7.8 nm. The intensity of the sound at the earhole is 4.8 × 10⁻⁷ W m⁻².

Determine the power of the sound incident at the earhole by estimating the diameter of the earhole in mm.

diameter of earhole ≈........ mm

A different sound wave is now incident at the ear. The intensity of this wave is 9.6 × 10⁻⁷ W m⁻².

Calculate the amplitude A in nm of this sound wave.

State the principle of superposition.

The diagram below shows monochromatic light from a laser incident normally at a double-slit.

The diagram is not drawn to scale.

A small light-detector is mounted onto a trolley on a frictionless track. The trolley travels along the track at a constant speed.

The separation between the slits is 0.20 mm. The perpendicular distance between the slits and the track is 8.2 m.

A series of bright and dark fringes are detected at the moving light-detector.

Explain, in terms of phase difference, the origin of the fringes.

The half-life of the isotope carbon-14 is 5700 years (y).

Carbon-dating is a technique used to date an ancient wooden axe. The ratio of carbon-14 to carbon-12 in the axe material is 78% of the current ratio of carbon-14 to carbon-12 in a living tree.

Calculate the age in years of the wooden axe.

State one assumption made in the calculation in (ii).

The diagram below shows two long vertical current-carrying wires X and Y.

The direction of the current in each wire is the same.

Explain why wire Y experiences a force and deduce the direction of this force.

State Faraday’s law of electromagnetic induction.

The diagram below shows the arrangement of the 3 protons inside the nucleus of lithium-6

The separation between each proton is about 1.0 × 10⁻¹⁵ m.

Calculate the magnitude of the repulsive electric force F experienced by the proton P

Explain how protons stay within the nucleus of lithium-6.

A spherical metal dome shown below is charged to a potential of −12 kV.

The dome is supported by a cylindrical plastic rod. The radius of the dome is 0.19 m.

Show that the magnitude of the total charge Q on the dome is 2.5 × 10⁻⁷ C.

The dome discharges slowly through the plastic rod. It takes 78 hours for the dome to completely discharge.

1 Show that the mean current I in the plastic rod is about 9 × 10⁻¹³ A.

2 The average potential difference across the plastic rod during discharge is 6000 V. The rod has cross-sectional area 1.1 × 10⁻⁴ m² and length 0.38 m.

Calculate the resistivity of the plastic.

=........ m

The medical tracer technetium-99m is used in imaging organs such as the brain.

Explain the advantages of using technetium-99m for this purpose.

A gamma-camera uses powerful computers and sophisticated software to produce three-dimensional images of the patient’s organ.

Name and describe the remaining three main components of the gamma camera.

X-ray photons interact with atoms.

The attenuation coefficient against lg(photon energy) graphs for simple scattering (S), photoelectric effect (PE), Compton effect (C) and pair production (PP) are shown below.

With the help of a calculation, explain the minimum photon energy shown on the graph for pair production.