P2 Unit 5 5.2 Resistance & 5.3 current potential difference graphs

Additional Science P2 Unit 5: Current electricity.

Lesson 2: Resistance & current-potential difference graphs

Textbook section P2 5.2 & 5.3

Aim: How do wires, filament lamps, diodes, LDR’s & thermistors affect the resistance in an electrical circuit?

Starter (10 min):
Students recap last lesson by answering summary questions 1 & 2 on pg 237 of the textbook. Mr C will provide the answers and students should self assess their work.

Main Activity 1 (20 min): Current/Potential difference graphs for wires, filament lamps and diodes.

Students are given some data and have to draw a current/potential difference graph for the above components. Mr C will provide the data but students can use their own data for wires and filament lamps if they completed the experiment from last lesson. Students should note the shape of the graphs.

Provided the temperature is kept constant the resistance of a wire is always the same. Because R = V/I the resistance (slope of the graph) is always a straight line through the origin of the graph.
The current-potential difference graph for a filament lamp curves. So the current is not directly proportional to the potential difference. Resistance in a filament lamp increases as the filament lamp heats up, so resistance increases when current increases. Reversing the direction of the current makes no difference to the shape of the graph.
The current through a diode flows in one direction only. In the reverse direction the diode has a very high resistance so the current is virtually zero.

Main Activity 2 (20 min): Thermistors and LDR’s

Mr C will describe how Thermistors and Light dependent resistors affect electrical circuits using Virtual Physics Laboratory.
Students then have to match the five components discussed today to descriptions of their effects on electrical circuits.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electricity/resistancerev3.shtml more information from BBC Bytesize.

Plenary (5 min): Four key questions

From Physics revision cards.

AQA Specification: Unit Physics 2.13.6

P2 Unit 5 lesson 1 Resistance & p.d/current graphs

Resistance & current/voltage graphsLesson P2 5.1/2/3

Aim: Calculate resistance (ohms) and draw current/p.d graphs for a wire, filament lamp and a diode.
Key words: Potential difference, resistance, voltage (p.d), current, filament lamp, diode.

Starter: Recap of circuits and introduction to Resistance equation...
Resistance (ohms) = Potential difference (Volts)/current (amperes).
R = V/I. Students try some examples to practice using the equation.

Main: Mr C will introduce current/p.d graphs and quickly demonstrate the circuit that you will need to set up. You will be changing the voltage in the circuit and measuring the effect this has on the current using an ammeter. You will then need to record your results in a table and plot them on a graph. The slope of the line represents the resistance in the circuit. Make sure you investigate the effect that wires, filament lamps and diodes have on resistance.
Write a short conclusion that summarises your observations. How do the various appliances effect resistance in electrical circuits (the slope of the graph).

Plenary: Mr C will go over what you should have observed during the experiment. Make sure you assess your own work so you know your understanding is correct.
To end the lesson Mr C will explain how thermistor’s and LDR’s (Light dependent resistors) affect resistance in a circuit. If there is time the summary questions on pg 239 of the textbook can be attempted.

Homework: from H/W book.

AQA Specification Link up
Physics 2.13.6