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.
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
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