- Students should be able to explain that, for some resistors, the value of R remains constant but that in others it can change as the current changes.
The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes.
The resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.
The resistance of a filament lamp increases as the temperature of the filament increases.
The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.
The resistance of a thermistor decreases as the temperature increases. The applications of thermistors in circuits eg a thermostat is required. The resistance of an LDR decreases as light intensity increases.
WS 1.2 Use a variety of models such as representational, spatial, descriptive, computational and mathematical to solve problems, make predictions and to develop scientific explanations and understanding of familiar and unfamiliar facts.
WS 1.4 Explain everyday and technological applications of science; evaluate associated personal, social, economic and environmental implications; and make decisions based on the evaluation of evidence and arguments.
MS 4c - Plot two variables from experimental or other data
MS 4d -Determine the slope and intercept of a linear graph
MS 4e - Draw and use the slope of a tangent to a curve as a measure of rate of change
AT 6 -Use of appropriate apparatus to measure current, potential difference (voltage) and resistance, and to explore the characteristics of a variety of circuit elements (links to A-level AT f).
- Resistance wire (full length glowing across classroom)
- 3 x
- 2 x small diameter straw
- 1 x large diameter straw
For practical :
- 1 x Variable resistors (large coiled ones)
- 1 x spider packs
- 1 x ammeter
- 1 x voltmeter
Students use the straws to model resistors, also if they are in parallel it is easier to blow
Students will then take various readings of a variable resistor to calculate the resistance at that point. (skills necessary for required practicals)