OCR A Level Physics B (Advancing) Practical skills in physics June 2018 question paper H557/03

A student uses the circuit shown in Fig. 1 to investigate the characteristics of a filament bulb.

Show that the resistance R of the filament bulb Y in this circuit is approximately 2 .

The bulb is broken and the diameter of the filament wire is measured. The diameter is found to be 0.046 ± 0.002 mm.

Calculate the cross sectional area A of the wire and the uncertainty.

=........ ±........ m² A

The filament is removed from the bulb housing and the length is measured to be 20 cm. Using your answer from (a)(i) calculate the conductivity of the filament of the bulb stating any assumption(s) that you make.

* A new working identical bulb is put in the circuit in Fig. 1. The resistor X is changed to one with a resistance of 6.9 . A student calculates that the voltage across resistor X will now be 6.0 V. Using ideas about current, temperature and the structure of metals explain whether or not the student is correct.

An experiment is carried out to find the half-life of a solid radioactive isotope X which emits beta radiation.

Describe two safety precautions necessary for handling such a material in the laboratory.

The results obtained from the experiment are given in the table below.

Explain what is meant by “Corrected count rate” and complete this column in the table.

Complete the fourth column of the table by calculating the missing values for ln (A / Bq).

A graph of ln (A / Bq) (y-axis) and t (x-axis) is drawn in Fig. 2. Plot the remaining points on

the graph and draw the line of best fit.

* Use your graph to find the value of half-life for the radioactive isotope X and explain the

advantages of using ln (A / Bq) against t over an A against t graph to find half-life.

In 1917 Robert Millikan investigated the motion of tiny oil drops in an electric field and used this to determine the charge on the electron. He sprayed tiny oil drops between two parallel metal plates connected to a high voltage power supply and observed their motion. The experiment was set up as shown in Fig. 3.

As the oil drops are forced through a spray nozzle they become negatively charged. With switch S open there is no potential difference between the plates and the oil drop is observed to be falling at constant velocity through the air.

Explain why the oil drop falls at constant velocity through the air.

The switch S is closed and the potential difference is adjusted until the oil drop remains stationary between the two parallel plates.

The following data are recorded:

potential difference V = 390 V distance between the plates d = 6.0 mm mass of an oil drop m = 2.15 10⁻¹⁵ kg.

Calculate the electric field strength E between the two parallel plates. Include a suitable unit.

Calculate the charge q carried by each oil drop.

This calculation does not take into account the effect of buoyancy from the displaced air. This effect produces an additional upwards force on the oil drop. Explain what effect this would have on the value calculated for charge.

The charge on the parallel metal plates is reversed. Explain the effect this has on the motion of the oil drop.

This question is about an experiment to determine the Young modulus of a copper wire. The diameter D of the wire was measured using a micrometer screw gauge in several places along the length of the wire. The values obtained are shown in the dot-plot shown in Fig. 4.1. Each dot represents one reading.

Use the information in the dot-plot to find the mean D. Use the spread to determine the percentage uncertainty.

mean D = ………………………… mm ± ……………… %

Calculate the cross sectional area A of the wire and include the uncertainty.

A marker is placed to give an original length of the wire as 4.00 ± 0.02 m. Fig. 4.2 shows the extension x of a metal wire at different applied loads F. x is measured to ± 0.5 mm and F is measured to ± 0.2 N. Fig. 4.2 shows the force-extension graph for the wire.

On Fig. 4.2 1 complete vertical and horizontal error bars on each of the plots 2 label the regions of elastic and plastic deformation

3 draw a line of best fit through the straight section of the graph.

Use the graph and the data given to calculate the value of the Young Modulus E. Include the appropriate unit.

* Use Fig. 4.2 and your answer to part (b)(ii) to estimate the percentage uncertainty in the calculated value of the Young Modulus and describe the main sources of error in the

experiment. Suggest and explain possible improvements to the experiment.