AQA PHA6 b6 x TN JUN14

• Charge C1by connecting flying lead 1 to S1; record voltmeter reading, ε • Discharge C1by connecting flying lead 1 to S2 • Starting the watch when the voltmeter reads 80% of εdetermine

June 2014

(Specifications A and B)

Unit 6 Investigative and Practical Skills in A2 Physics

Route X Externally Marked Practical Assignment (EMPA)

The Exams Officer should make two copies of these Teachers’ Notes; one copy for the

Head of A-level Physics and one for the technician.

These copies can be released to the Head of A-level Physics and the technician at any point following publication but must be kept under secure conditions at all times.

Teachers can have sight of the Teachers’ Notes but no further copies should be made.

Estimated entries must be submitted to AQA in order for centres to receive hard copies of the materials to be used by candidates.

For Section A Task 1, Question 1 and Question 2

In Question 1, candidates will investigate capacitor discharge through a resistor In Question 2, they will investigate how the pd across a capacitor, C1, varies as it is discharged through a combination of

a resistor and a second (initially uncharged) capacitor, C2

The circuit to be provided for each candidate is shown below

Candidates will carry out the following procedure:

Question 1:

• Ensure that C2remains discharged by connecting flying lead 2 to S3

• Charge C1by connecting flying lead 1 to S1; record voltmeter reading, ε

• Discharge C1by connecting flying lead 1 to S2

• Starting the watch when the voltmeter reads 80% of εdetermine the times for the voltmeter reading to reach 40% of εand 20% of ε

Question 2:

• Remove flying lead 1 from S2

• Connect flying lead 2 to S2to avoid accidential discharge of C2 by earthing etc

• Charge C1by connecting flying lead 1 to S1

• Discharge C1by connecting flying lead 1 to S3; recording the voltmeter reading at 10 s intervals

Apparatus required for each candidate:

• dc power supply, terminal pd at the discretion of the Centre; if the voltmeter is set to the

2000 mV range then one type D cell in good condition, in a suitable holder, will be adequate

• digital voltmeter with high input impedance (>1 MΩ) set to a range that will suit the power supply the Centre wishes to use; a 31⁄2digit LCD multimeter set to the 2000 mVrange will be adequate if a 1.5 Vdry cell is used

• one 12 kΩcarbon film resistor, at least 0.25 W; the resistance of this resistor should be

concealed from the candidates

• one 1000 μFelectrolytic capacitor, 10 Vor higher, labelled ‘C1’

• one 2200 μFelectrolytic capacitor, 10 Vor higher, labelled ‘C2’

• three round sockets to be labelled ‘S1’, ‘S2’ and ‘S3’

• suitable connecting leads, including two flying leads, each terminating with a 4 mm round plug connected as shown in the circuit diagram below; these should be labelled as indicated

• digital stopwatch capable of reading to 0.1 sor better

• card on which the calculated capacitance of C1should be provided for the candidate’s use

digital voltmeter

socket S2

labelled ‘C1’

labelled ‘C2’

flying lead 1

V

flying lead 2

Turn over䊳

Testing:

In Question 1, C2is redundant; the exercise is to charge and then discharge C1through R

Candidates will require the capacitance of C1that they will use and this can be found directly using

a capacitance meter, or indirectly by measuring the time for the voltmeter reading to fall to 50%of some initial value The capacitance of C1(in F) is given by

time (in seconds) for voltmeter reading to halve

8.32 × 103 The time for the voltmeter reading to halve will typically be between 7.5 sand 10.5 s

In Question 2 parts (a)(i) and (a)(ii), the voltmeter reading will decrease at a decreasing rate when the flying lead 1 is connected to S2 The pd across C2rises to meet the (falling) pd across C1and when these equalise the voltmeter reading will become approximately constant; this takes about 50 s and the reading will be equal to 30%to 35%of the initial reading

In Question 2 parts (a)(iii) and (a)(iv) the reading falls more gradually than before because C2is already charged from part one Once again, the process stops when the pd across C1is the same

as across C2; this time the voltmeter reading will reach an approximately constant value about 50%

of the initial reading

Place all the apparatus required on the bench before the experiments with both flying leads

disconnected and the card giving the calculated capacitance of C1in clear view

Examiners require no information for this question.

The following data are provided to assist in trialling the practical tasks

Question 1

(a)

Question 2

(a) and (b)

C1 =

voltmeter

reading time/s

40% of ε 9.52

20% of ε 18.67

t/s VA/V VB/V

For Section A Task 2

Candidates are to measure the time period of a simple pendulum with an interrupted swing

The working arrangement is shown in Figure 5 of the question/answer booklet.

The apparatus is to consist of a simple pendulum of length 0.90 msuspended so that the thread overhangs the edge of the bench The thread is to pass through the hole in the terminal post, so by unscrewing the terminal the thread is released and candidates can change the effective length of the pendulum At a point 250 mmbelow the shoulder of the terminal, a section of plastic ruler is mounted horizontally so the tapered edge of the ruler interrupts the pendulum at the mid-point of its swing The motion of the pendulum in a plane perpendicular to the edge of the bench will therefore consist of half cycles of different duration

The suggested arrangement for the apparatus is described and illustrated in the diagram as follows Drill a suitable hole through the median line of the m.d.f to accommodate the threaded stem of the terminal post Fit the terminal post in place then trim the m.d.f so the distance between the

shoulder of the terminal post and the end of the m.d.f is 250 mm Glue the section of ruler in place

so that approximately 4 mm protrudes Assemble the pendulum by passing the thread through the hole in the terminal post and tie on the bob Fasten a small washer to the (upper) free end of the thread to prevent the thread becoming detached from the terminal post when the terminal is

unscrewed

Apparatus required for each candidate:

• digital stopwatch capable of reading to 0.1 sor better

• metre ruler

• pendulum bob fastened to about 1 metre of strong thread (which should resist stretching)

• suitable fiducial mark to assist candidates to measure the period of the pendulum

• retort stand fitted with boss and clamp

• means to prevent stand movement if required

Materials to construct assembly to support the interrupted pendulum:

• rectangular strip of thin sheet material, eg 12 mm m.d.f., suitable dimensions 300 mm × 40 mm

• between 30 mmand 40 mmof a plastic ruler (which could be cut along median line)

• one 4 mm binding (terminal) post

• small washer

Clamp the m.d.f so that the pendulum overhangs the edge of the bench The terminal post should

be about 100 mm above the top of the bench Adjust the length of the pendulum so that the bob hangs freely about 100 mm above the floor and when the thread is at rest and hanging vertically it just touches the protruding edge of the ruler

The metre ruler, stopwatch and fiducial mark should be placed on the bench alongside the

apparatus

For candidates with mobility problems the apparatus can be mounted on a tall stand so that the experiment can be carried out at bench level

Examiners require no information for this question.

The following data are provided to assist in trialing the practical tasks

Question 1

(a) x/m= 0.248

(b)

250mm

terminal post

washer

12 mm m.d.f or similar

section of plastic ruler

Turn over䊳

General Certificate of Education

June 2014

Advanced Level Examination

PHYSICS (SPECIFICATIONS A AND B) PHA6/B6/XTN

Unit 6

SUPERVISOR’S REPORT

When completed by the Supervisor, this Report must be attached firmly to the attendance list, or in the case of any problem affecting a particular candidate, it should be attached to the candidate’s script, before despatch to the Examiner.

Details of problems encountered by candidate candidate number

Supervisor’s Signature Centre number

Date

Centres may make copies of this Supervisor’s Report for attachment to individual scripts where necessary.

her use only

The following instructions include the tasks that candidates will be required to complete in Section A Task 1 and Section A Task 2 These instructions do not include all the questions that may be asked

Section A Task 1

1 You are to determine the resistance of a resistor Rof unknown resistance using the

circuit shown in Figure 1.

Figure 1

This circuit is used for both Question 1 and Question 2 in Section A Task 1

Connect flying lead 2 to socket S3 as shown in Figure 1; Keep this lead connected to

S3whilst making the measurements in Question 1.

1 (a) Connect flying lead 1 to socket S1so that capacitor C1is fully charged

1 (a) (i) Read and record the voltmeter reading, ε

ε=

Turn over䊳

digital voltmeter

socket S1

socket S2 socket S3

C1

R

C2 flying lead 1

V

flying lead 2

her use only

1 (a) (ii) Remove flying lead 1 from socket S1and connect this without delay to socket S2so the

voltmeter reading decreases as C1discharges through resistor R

Start the stopwatch when the voltmeter reads 80%of ε

Measure and record, the times at which the voltmeter reads 40%and 20%of ε

2 (a) Disconnect flying lead 1 from S2.

Connect flying lead 2 to S2as shown in Figure 3; keep this lead connected to S2whilst making the measurements in Question 2 (unless you wish to discharge C2in order to repeat the question)

You are not required to take any repeat readings in Question 2(a)

Figure 3

2 (a) (i) Charge C1by connecting flying lead 1 to S1

Record the voltmeter reading, VA

2 (a) (ii) Disconnect the lead from S1and without delay connect it to S3, starting the stopwatch as

you do this.

Read and record further values of VAat 10 second intervals

2 (a) (iii) Remove flying lead 1 from S3and connect it to S1to recharge C1

Record the voltmeter reading, VB

2 (a) (iv) Disconnect the lead from S1and without delay connect it to S3, starting the

stopwatch as you do this

Read and record further values of VBat 10 second intervals

You are not required to repeat the experiment but should you need to do so,

disconnect flying lead 1 from S3and flying lead 2 from S2

Briefly connect flying lead 2 to S3to discharge C2before reconnecting this lead

to S2 You may now recommence the procedure starting at part 2 (a)(i)

digital voltmeter

socket S1

socket S2 socket S3

C1

R

C2 flying lead 1

V

flying lead 2

her use only

Section A Task 2

1 In this experiment you are required to measure the time period of a pendulum with an

interrupted swing

You are provided with the apparatus shown in Figure 5, including a fiducial mark.

Figure 5

Turn over䊳

Piece of ruler

Pendulum bob

l

x

A

B Terminal

Washer

her use only

1 (a) Measure and record x, the length of thread between the terminal and the piece of ruler

x = .

1 (b) Holding the washer in one hand, unscrew the terminal Adjust l, the length of the thread

between the piece of the ruler and the centre of the pendulum bob, until lis about 0.55 m Secure the thread in this position by tightening the terminal

Make further adjustments to ensure that when the pendulum is at rest the string is vertical along its entire length and just touches the edge ABof the ruler

Measure and record l

Displace and release the pendulum so that it performs small-amplitude oscillations in a plane perpendicular to AB

Make suitable measurements to determine the period, T, of these oscillations

Repeat this procedure to find Tfor four smaller values of l

Record all your observations

Note that the independent variable should be recorded in the left-hand column of your

table