Student starting points - charge flow
Teaching Guidance
for 14-16
Diagnostic question on ammeter readings
The following question, on electrical current, was set to a group of students after their 11–14 teaching on electric circuits:
In this circuit the ammeter at position 1 reads 0.3 ampere. Predict the value of the current at positions 2 and 3.
Current at ammeter 2 is …
Current at ammeter 3 is …
Explain why you have predicted these values.
Correct answers:
Current at ammeter 2 is 0.3 ampere
Current at ammeter 3 is 0.3 ampere
Explanation:
The current is the same in every element round this simple series circuit. This is because the rate of flow of charge (the number of coulombs of charge passing each point every second) is the same for every point in the circuit.
Some students' answers and implications
Student 1
Ammeter 2: 0.6
Ammeter 3: 0.3
Because the energy in the charges go past the ammeter with energy in the charges then when it gets to number 2 the charges are empty so it is low.
Student 2
Ammeter 2: 0.3 ampere
Ammeter 3: 0.3 ampere
Because the flow of energy will be the same all the time and the bulbs will be dim.
Student 3
Ammeter 2: 0.3 ampere
Ammeter 3: 0.3 ampere
Because all the current has been shared equally.
Student 4
Ammeter 2: 0.3 ampere
Ammeter 3: 0.3 ampere
I predicted these values because the current stays the same speed all the time.
Student 5
Ammeter 2: 0.3 ampere
Ammeter 3: 0.3 ampere
No explanation given.
Thinking about the teaching
Although four out of five students give correct predictions of the value of the current, the explanations do not inspire confidence! At least some student answers are off down the wrong tracks.
Students 1 and 2 refer to energy
in their explanations, possibly getting mixed up with ideas of voltage. The way in which student 3 refers to the current being shared seems closer to an explanation for a parallel circuit. The answer given by student 4 is more encouraging, although it would be preferable to say the charged particles drift along at the same rate everywhere
.
