Edexcel A Level Physics Paper 3: General and Practical Principles in Physics June 2017 question paper 9PH0/03

A physics textbook states that “when carrying out experimental measurements there will always be errors and uncertainties”.

Describe what physicists mean by error and by uncertainty.

Give two reasons why a measurement may have an uncertainty.

A student carries out measurements to determine the density of glass. The student has 20 glass microscope slides available.

The approximate dimensions of one slide are shown.

The density is calculated using the equation

Describe how the student can determine an accurate value for the density of the glass. Your answer should include the measuring instruments required.

State one precaution that the student should take to ensure the measurements are accurate.

In the 19th century experiments with magnetic and electric field deflections were used to determine the charge to mass ratio of electrons. Later experiments showed the diffraction of electrons as they passed through thin metal foils. Deduce what these experiments tell us about electrons.

A student set up a “seconds pendulum”. This is a simple pendulum for which the time taken to move from the bob’s highest position on one side to its highest position on the opposite side is 1.00 s.

Calculate the length L required for the pendulum to be a “seconds pendulum”.

The student set the pendulum into oscillation. She used a stopwatch to check the accuracy of the pendulum’s period T.

Describe the procedure the student should have used to obtain an accurate value for T.

Another student suggested that the uncertainty in the measurement of the time period of the pendulum could be reduced by using a light gate and a data logger. The data logger would record the time between successive interruptions of the light beam. Both the data logger and the stopwatch have a resolution of 0.01 s.

Comment on the student’s suggestion of using a data logger rather than a stopwatch.

*5 The following extract comes from a section on forces, on a website written for children.

Criticise this extract.

A student carried out an experiment to determine the resistivity of nichrome wire.

He used an ohmmeter to measure the resistance of a length of nichrome wire as shown.

The diameter of the wire was measured as 0.27 mm ± 0.01 mm. The length of the wire was measured as 1.25 m ± 0.05 m.

Determine which of the three measurements introduces the greatest uncertainty into the value for the resistivity. Your answer should include calculations.

Explain how the student could reduce the uncertainty in the measurement of the diameter.

Calculate the minimum value of resistivity possible from the student’s data.

A teacher is demonstrating how to measure the speed of sound in a steel rod. The equipment comprises a hanging steel rod and a hammer connected to a data logger as shown.

The rod is tapped at A with the hammer. A compression pulse travels to B and is reflected back. When the reflection reaches A the hammer loses contact with the rod. Whilst the hammer is in contact with the rod the output from a 5 V supply is recorded by the data logger.

The graph shows the output from the data logger for one hammer tap.

Explain why a data logger is appropriate for this demonstration.

Use the graph to show that the speed of the pulse in the rod is about 6000 m s⁻¹.

length of steel rod = 1.18 m

The speed of sound v in the rod depends on the Young modulus E and the density ρ of the material of the rod as given by the equation

Calculate the Young modulus of steel.

ρ_steel= 7850 kg m⁻³

A student wanted to plot a graph of current against potential difference for a light emitting diode (LED). He used the circuit shown.

Add an ammeter and a voltmeter to the circuit diagram that would enable the data to be collected.

The graph of current against potential difference obtained by the student is shown.

The student wrote the following conclusion.

“The graph shows that in general the LED is not an ohmic conductor. However, for potential differences greater than +2 V, Ohm’s law is obeyed since the graph is linear in this region.”

Criticise the student’s conclusion.

The student used the LED with a 5.0 V power supply as shown in the circuit.

To be lit to normal brightness the current through the LED must be 18 mA.

Calculate the resistance of the resistor needed in the circuit.

The majority of stars in the universe are thought to be main sequence stars. For such stars the luminosity increases with the mass of the star.

It is suggested that the relationship between luminosity and mass is of the form

where L = luminosity, M = (mass of star / mass of the Sun) and L_Sun and p are constants. Explain why a graph of log L against log M would give a straight line.

The table shows data for a range of main sequence stars.

Plot a graph of log L against log M. You may use the columns provided to show any processed data.

Determine values for p and L_Sun and hence state the mathematical relationship between L and M.

A student investigated the way in which gamma radiation spreads out from a source. He placed a cobalt-60 source in a source holder and set up a Geiger-Müller (GM) tube a short distance d away. He connected the GM tube to a counter as shown.

The student recorded the count for 2 minutes.

Describe how to determine the corrected count rate from the source.

His teacher turned the GM tube through 90° so that the side of the tube faced the source as shown below.

Explain why this arrangement could lead to more accurate data.

Explain another modification to the experimental method which would improve the accuracy of the data.

The variation in the intensity of gamma radiation with distance from a point source should obey an inverse square law. If this is the case, then the count rate C should vary with d according to the equation

where K is a constant. The student plotted against d and obtained the following graph.

Draw a line of best fit on the graph.

The student concluded that the graph was consistent with the gamma radiation intensity obeying an inverse square law.

Discuss the extent to which the data obtained supports the student’s conclusion.

It is suggested that the investigation into the way in which gamma radiation spreads out from a source, using the apparatus as shown in (b), could be carried out successfully using a radium-226 source.

Radium-226 emits α, β and γ radiation.

Justify this suggestion.

A student investigated the behaviour of a spring under tension. The spring was hung vertically with a mass holder attached.

The position of the bottom of the mass holder was recorded. The spring was stretched by adding masses to the mass holder and the new positions were recorded. The extension of the spring each time was calculated.

The student produced the following table.

Criticise the student’s table.

The student used her data to plot a graph as shown.

Determine a value for the force constant k of the spring.

Two identical springs are joined in series and a bar magnet is hung from one end as shown.

The bar magnet is displaced a small distance vertically from its equilibrium position and released.

Calculate the frequency at which the system oscillates.

mass of magnet = 120 g spring constant of each spring = 22 N m⁻¹

*(d) Identical bar magnets are suspended from identical springs, with the North pole of each magnet inside a coil of wire as shown. The two coils are connected together with conducting leads.

Magnet A is displaced so that it oscillates vertically. The North pole of magnet A moves into and out of the coil of wire with simple harmonic motion. As this motion continues, magnet B starts to oscillate. The amplitude of oscillation of magnet B increases over time.

Explain why magnet B starts to oscillate with an increasing amplitude.

Barnard’s star is a red dwarf star in the vicinity of the Sun. The wavelength of a line in the spectrum of light emitted from Barnard’s star is measured to be 656.0 nm. The same light produced by a source in a laboratory has a wavelength of 656.2 nm.

Calculate the velocity of Barnard’s star relative to the Earth.

A diffraction grating can be used to analyse the radiation emitted by a variety of sources.

A diffraction grating of known grating spacing is used in a school laboratory to analyse the light emitted by a laser.

Describe how the diffraction grating is used and the measurements that should be taken.

A diffraction grating with grating spacing of 2.2 × 10⁻⁶ m is used to determine the difference in wavelength for the spectral line emitted by Barnard’s star.

Comment on the suitability of using a diffraction grating with this spacing. You should include appropriate calculations.

Visible light from the star originates from the photosphere. In the photosphere of Barnard’s star, hydrogen and helium atoms are at a temperature of 3100 K.

Calculate the mean kinetic energy of an atom in the photosphere at a temperature of 3100 K.

Describe how these atoms emit visible light.

Mass spectrometry is a technique used to separate ions based on their charge to mass ratio.

The atoms in a sample are ionised and then accelerated and formed into a fine beam. This beam is passed into a region of uniform magnetic field and the ions are deflected by different amounts according to their mass.

Analysis of mass spectrometer data shows that chlorine exists in nature as two isotopes, chlorine-35 and chlorine-37.

State what is meant by isotopes.

In a mass spectrometer, chlorine-35 ions are accelerated through a potential difference of 8.50 kV to produce an ion beam.

Show that the speed of singly ionised chlorine-35 atoms is about 2.2 × 10⁵ m s⁻¹.

mass of an ion of chlorine-35 = 34.97 u

In most mass spectrometers the ions are passed through a velocity selector, after being accelerated, to produce a beam of ions of a particular velocity. The velocity selector consists of a pair of parallel plates, across which a potential difference (p.d.) is applied to create an electric field.

In one mass spectrometer the plates are 2.5 cm apart and a p.d. of 135 V is applied.

A magnetic field is also applied to produce a force on the ions in the opposite direction to the force from the electric field. For one particular speed the ions travel in a straight line and emerge from the selector.

Add to the diagram to indicate the directions of the electric field and the magnetic field.

The magnetic flux density applied to the velocity selector is 24.5 mT.

Deduce whether this magnetic flux density is suitable to produce a beam of chlorine-35 ions of speed 2.2 × 10⁵ m s⁻¹.

After passing through the velocity selector the ion beam enters a region of uniform magnetic flux density 0.35 T with the ions travelling at right angles to the field direction.

Explain why the ions travel in a circular path.

Calculate the radius of the circular path.

The diagram shows the path of the chlorine-35 ions in the field. Chlorine-37 ions enter the magnetic field with the same velocity.

1. Add another line to the diagram to show the path of these chlorine-37 ions.

2. Explain any differences in the paths.