The table below shows readings from a student testing a 5.0 ohm resistor. Fig. 1 shows the circuit used. The student changes the variable resistor slowly an...
Question 1 Report
The table below shows readings from a student testing a 5.0 ohm resistor. Fig. 1 shows the circuit used. The student changes the variable resistor slowly and records the current and voltage once the resistor has stayed at a steady temperature. A graph of voltage against current can then be used to check whether the component obeys Ohm's law.
| voltage / V | current / A |
|---|---|
| 1.0 | 0.20 |
| 2.0 | 0.40 |
| 3.0 | 0.60 |
| 4.0 | 0.80 |
(a) State two variables that should be controlled during this test. [2]
(b) Calculate the resistance using the 3.0 V reading. [2]
(c) Explain why the graph is a straight line through the origin. [2]
(d) State the reading on the graph when the current is zero. [1]
(e) Describe one safety precaution for this circuit. [1]
Answer Details
(a) Two suitable controlled variables are the temperature of the test resistor and use of the same resistor [2]. The same connecting leads or the same meters are also acceptable. Controlling temperature matters because resistance can change if the resistor heats up.
(b) Use \(R=V/I\):
\[R=\frac{3.0\ \mathrm{V}}{0.60\ \mathrm{A}}=5.0\ \Omega\]
Resistance = \(5.0\ \Omega\) [2].
(c) A straight line through the origin means voltage is directly proportional to current [1]. This happens because the resistance remains constant, so the resistor obeys Ohm's law [1].
(d) At zero current, the graph reading is \(0\ \mathrm{V}\) [1].
(e) One suitable precaution is to switch off between readings [1]. This reduces heating and avoids unnecessary current flow. Using a low-voltage supply or not touching a hot resistor would also be acceptable.
Download The App On Google Playstore
Everything you need to excel in your exams
