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PreparationOhm’s law

Physics · Related practical

Ohm’s law

Measure current and potential difference, record your readings and investigate resistance.

Combined Science 4003/3, June 2019 · Question 2

Use this practical to study the skills in the linked examination question. The apparatus and samples practise the same ideas; they do not reproduce the examination setup exactly.

A Level · Form 5 · 30 minutes

Learning objectives

  • Read current and potential difference at several supply settings
  • Calculate resistance using voltage divided by current
  • Plot potential difference against current
  • Use the gradient and repeated readings to judge whether resistance is constant
Practical mode

Guided gives instructions as you work. Practice lets you choose your method.

Source paper

Original examination paper

Combined Science · Paper 3

4003/3 · JUNE · 2019 · 1 hour 30 minutes

Read the complete original paper below. The related question is identified in this practical’s introduction.

Unattributed annotation: CHIPIRO MARTIN TATENDA
mtchipiro@gmail.com
0774 382 888

ZIMSEC
For Development

Candidates answer on the question paper

Additional materials:

As listed in instructions to Supervisors
Calculator (optional)

INSTRUCTIONS TO CANDIDATES

Write your name, centre number and candidate number in the spaces at the top of this page.

Answer both questions.

Write your answers in the spaces provided on the question paper.

Use a sharp pencil for your drawings. Coloured pencils or crayons should not be used.

You should record all experimental results and show the essential steps in any calculation in the spaces provided in the question paper.

INFORMATION FOR CANDIDATES

The number of marks is given in brackets [ ] at the end of each question or part question.

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Unattributed annotation: CHIPIRO MARTIN TATENDA
mtchipiro@gmail.com
0774 382 888

1.[20 marks]

You are required to identify nutrients present in juice X.

You are provided with three boiling tubes, a test tube rack, a pair of tongs, a graduated syringe, Benedict's solution, hot water bath, juice X, solution P, solution R and access to a clock.

a)[18 marks]

i)[10 marks]

Carry out the tests described in Table 1.1 below and record the observations and deductions in the table.

Table 1.1

testobservationsconclusions
Add about 2 cm³ of juice X into a boiling tube and add two drops of solution R to the juice.
Place about 2 cm³ of juice X into a clean boiling tube and add about 2 cm³ of Benedict's solution to the juice.<br><br>Heat the mixture in a water bath.
Place about 3 cm³ of juice X into a clean boiling tube and add about 4 cm³ of solution P to the juice.<br><br>Place the test tube in the hot water bath and leave it for about 3 minutes.<br><br>After the 3 minutes, pour about half of the contents into another clean boiling tube.<br><br>Add two drops of solution R to one of the portions.
Add about 2 cm³ of Benedict's solution to the other portion and heat in the water bath.

ii)[1 marks]

Identify solution R.

iii)[1 marks]

State the colour of Benedict's solution.

iv)[2 marks]

State the nutrients contained in juice X.

v)[1 marks]

Suggest one advantage of drinking juice X.

vi)[1 marks]

Suggest a possible identity of solution P.

vii)[1 marks]

State the process responsible for the change that occurred when solution P was added to the juice and the mixture heated.

viii)[1 marks]

Name the part of the alimentary canal where the process mentioned in (vii) occurs.

b)[2 marks]

State any two precautions that should be taken when carrying out the experiment.
Unattributed annotation: Scanned by CamScanner

Unattributed annotation: CHIPIRO MARTIN TATENDA
mtchipiro@gmail.com
0774 382 888

Unattributed annotation: Scanned by CamScanner

Unattributed annotation: CHIPIRO MARTIN TATENDA
mtchipiro@gmail.com
0774 382 888

2.[20 marks]

a)[18 marks]

You are required to determine the resistance of a wire, R. Fig.2.1 shows the circuit diagram for the circuit which the supervisor set for you.
Circuit diagram for the circuit which the supervisor set for you.
Circuit diagram for the circuit which the supervisor set for you.

i)[10 marks]

Place one cell in the cell holder, close the switch and record the voltmeter and ammeter readings in Table 2.1. Repeat the procedure adding one cell at a time until you use four cells.

Table 2.1

number of cellsvoltage/Vcurrent/A

ii)[3 marks]

Plot a graph of voltage (y-axis) against current (x-axis).
Blank graph grid for plotting voltage against current.
Blank graph grid for plotting voltage against current.

iii)[1 marks]

State the relationship between voltage and current.

iv)[2 marks]

Calculate, using the graph, the resistance of wire R.

v)[2 marks]

Determine, clearly showing on the graph, the current when the voltage is 3.5 V.

b)[2 marks]

State any two sources of error in the experiment.
Unattributed annotation: Scanned by CamScanner

Unattributed annotation: CHIPIRO MARTIN TATENDA
mtchipiro@gmail.com
0774 382 888

Unattributed annotation: Scanned by CamScanner

Unattributed annotation: CHIPIRO MARTIN TATENDA
mtchipiro@gmail.com
0774 382 888

Unattributed annotation: Scanned by CamScanner

Study notes

Overview

Find how current changes as the voltage across a resistor changes. Take several pairs of meter readings, calculate resistance and use a graph to check whether it stays constant.

Method

1. With the switch open, select the supply and set a small positive voltage.
2. Close the switch briefly. Read and enter current and potential difference, then open it.
3. Calculate V/I and enter your resistance. New trial opens the switch and retains voltage. Vary voltage and repeat.
4. Plot potential difference vertically against current horizontally. Interpret the gradient and explain whether resistance is constant.

Selection, visible controls and Shift shortcuts share operations. Fields save valid entries on Enter, Tab or leaving the field. Check a calculator result before saving it. Reopening an earlier trial restores entries without moving the apparatus.

Safety and measurement

Use the low-voltage supply and open the switch before adjustment. Open between readings to limit heating in real equipment. The model holds resistor temperature fixed and omits heat loss and damage. Session expiry stops circuit operation and preserves recordings.

Analysis

Calculate resistance from your recorded values:

R=VIR=\frac{V}{I}

Use volts and amperes to obtain ohms. Do not divide by zero current. Plot voltage on the vertical axis and current on the horizontal axis. The gradient is ΔV/ΔI\Delta V/\Delta I, in ohms. Reversing the axes gives conductance instead.

The calculator uses copies of your saved readings. Inserting a result leaves a draft for you to finish. Analysis shows partial saved points immediately; repeat trials strengthen the evidence.

Practice quiz

Answer all questions, then check your answers and read the explanations.

1
Where does the ammeter go?
2
Where does the voltmeter go?
3
Which calculation gives resistance?
4
Which unit is resistance?
5
What belongs on the vertical axis in this investigation?
6
What is the unit of this graph gradient?
7
Which condition should remain constant for an ohmic conductor?
8
What should you do before changing the supply?
9
Can V/I give resistance when the switch is open and both readings are zero?
10
Why take more than one voltage-current pair?