Charge and Current | OCR A-Level Physics A (H556)
Charge and Current
- 32 questions
- 3 subtopics
- Module 4: Electrons, waves and photons
- Paper 2 and Paper 3
What electric current is, the quantisation of charge, and the surprisingly slow drift of the electrons that carry it..
It covers electric current and the coulomb, elementary charge, charge carriers and Kirchhoff's first law and mean drift velocity.
Sample questions from Charge and Current
Answer each one closed book first, then open the answer.
-
Electric current and the coulomb
In the equation I = Q/t, what does each symbol represent?
Show the answer
I represents current, Q represents charge, and t represents time. -
Electric current and the coulomb
State the equation used to calculate charge from current and time.
Show the answer
Q = It, where Q is charge, I is current, and t is time. -
Elementary charge, charge carriers and Kirchhoff's first law
Why can an object never have a charge of 2.4 × 10⁻¹⁹ C?
Show the answer
Because charge is quantised and can only exist as integer multiples of e (1.6 × 10⁻¹⁹ C), and 2.4 × 10⁻¹⁹ C is not an integer multiple of e. -
Elementary charge, charge carriers and Kirchhoff's first law
State Kirchhoff's first law.
Show the answer
The sum of currents entering a junction equals the sum of currents leaving the junction. -
Mean drift velocity
In the equation I = Anev, what does the symbol n represent?
Show the answer
n represents the number density of charge carriers. -
Mean drift velocity
Why do insulators not conduct electricity well?
Show the answer
Insulators have a very low number density of charge carriers, so very few charges are available to move and carry current.
The 3 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Electric current and the coulomb | Recall questions on defining electric current, I = Q/t and Q = It with calculations, and the coulomb as the unit of charge. | 8 |
| Elementary charge, charge carriers and Kirchhoff's first law | Recall questions on the elementary charge and quantisation of charge, charge carriers in metals and electrolytes, conventional current and electron flow, and Kirchhoff's first law as conservation of charge. | 13 |
| Mean drift velocity | Recall questions on I = Anev, what each symbol stands for, and why drift velocity is so small. | 11 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
-
Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
-
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
-
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Physics A Active Recall Guide
Every topic, not just this one. 1,862 questions with their answers.