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School Physics GCSE level Notes: Electricity 3.5 Q = It calculation questions

Electricity Section 3:

3.5 Movement of charge - calculation of the charge passing through a point in a circuit,  Q = It calculation questions

[Author © Dr WP Brown PhD: Doc Brown's physics exam revision notes suitable for students of UK IGCSE & GCSE level physics courses, ~ US grades 9-10 physics, electricity page updated Feb 8th 2026]

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INDEX for electricity section 3 notes on current, voltage, resistance, energy & charge transfer in circuits

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ANSWERS to ALL the QUESTIONS at the end of the page

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3.5 Movement of electrical charge

Questions to be answered e.g. 

How do you calculate the amount of electric charge moving in a circuit?

Calculation of the charge passing through a point in a circuit Q = It

Current (I in amps) is the rate of flow of electrical charge around a circuit - coulombs (C) per second (s) past a given point in a circuit.

The greater the flow of charge in a given time the greater the current.

The rate of flow of electric charge is measured in coulombs/second.

You can calculate the charge passing a point in a circuit in a given time from the formula

Q = It

where Q = electric charge transferred in coulombs (C) unit of electric charge

I = current flow in amperes (A) and t = time (s)

rearrangements from Q = It,  I = Q/t  and  t = Q/I

It is better to be able to rearrange the Q = It equation, rather than use the triangle.

A current flow of 1 A equals a rate of flow of charge of 1 C/s.

 

Examples of calculation questions involving the equation Q = It

Q1 If a current of 3.0 A passes through an appliance for 1 hour and 30 minutes, how much electrical charge is transferred in the process?

ANSWERS

 

Q2 If 9000 C of charge passes a point in an electrical circuit in 12.0 minutes, what is the current flow?

ANSWERS

 

Q3 How long will it take, in minutes and seconds, for an electrical circuit current of 20.0 A to transfer 5000 C of charge?

ANSWERS

 

Q4 A laptop computer battery charger passes a current of 1.20 A for 30 minutes with an output p.d. of 15.0 V.

(a) Calculate how much charge is transferred to the computer battery.

(b) What is the resistance of the battery charger?

(c) When the laptop battery is fully charged it stores 3000 C.

How long will it take to fully charge a flat battery?

ANSWERS

 

INDEX of electricity section 3 notes on current, voltage, resistance, energy & charge transfer in circuits including Ohm's Law investigations

Key points about electric circuits in physics courses - calculations of charge transferred

Information sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks & syllabus-specifications for students taking the UK AQA, Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and CIE GCSE physics 9-1 level science examinations.

Keywords, phrases and learning objectives for the movement of electrical charge

Know that current (I in amps) is the rate of flow of electrical charge Q around a circuit.

Be able to do calculations of movement of charge in circuits from Q = It.

Know that current equals the rate of charge passing through a point in a circuit.

Know how to rearrange and use the equations Q = It, I = Q/t, t = Q/I in calculations, relating charge in charge in coulombs, time in seconds and current in amperes i.e. using the appropriate units.

SITEMAP

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ANSWERS to examples of calculation questions involving the equation Q = It

Q1 If a current of 3.0 A passes through an appliance for 1 hour and 30 minutes, how much electrical charge is transferred in the process?

Q = It,  Q = 3.0 x 1.5 x 60 x 60 = 16 200 C = 1.62 x 104 C

 

Q2 If 9000 C of charge passes a point in an electrical circuit in 12.0 minutes, what is the current flow?

I = Q/t = 9000/(12 x 60) = 9000/720 = 12.5 A

 

Q3 How long will it take, in minutes and seconds, for an electrical circuit current of 20.0 A to transfer 5000 C of charge?

t = Q/I = 5000/20 = 250 seconds = 4 mins and 10 seconds

 

Q4 A laptop computer battery charger passes a current of 1.20 A for 30 minutes with an output p.d. of 15.0 V.

(a) Calculate how much charge is transferred to the computer battery.

Q = It = 1.2 x 30 x 60 = 2160 C

(b) What is the resistance of the battery charger?

V = IR,  R = V/I = 15 / 1.2 = 12.5 Ω

(c) When the laptop battery is fully charged it stores 3000 C.

How long will it take to fully charge a flat battery?

Q = It, t = Q / I  = 3000 / 1.2 = 2500 s (41 min 40 secs)

INDEX of electricity section 3 notes on current, voltage, resistance, energy & charge transfer in circuits including Ohm's Law investigations

Website content © Dr Phil Brown 2000+. All copyrights reserved on Doc Brown's physics revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries and references to science course specifications are unofficial. Explaining the importance of calculation of moving charge Q=It questions in GCSE physics, What you need to know about calculation of moving charge Q=It questions for IGCSE physics, Explaining the use of calculation of moving charge Q=It questions knowledge in GCSE physics, Examples of calculation of moving charge Q=It questions explained for GCSE physics exams, What is the significance of calculation of moving charge Q=It questions in studying for physics exams, What is the use of calculation of moving charge Q=It questions ?  Describing and explaining the theory of calculation of moving charge Q=It questions, revision preparation for AQA GCSE physics, Edexcel GCSE physics, OCR GCSE physics. Website content © Dr Phil Brown 2000+. All copyrights reserved on Doc Brown's physics revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries and references to science course specifications are unofficial. These revision notes on calculation of moving charge Q=It questions are suitable for AQA gcse physics, calculation of moving charge Q=It questions revision notes for Edexcel gcse physics, calculation of moving charge Q=It questions revision notes for OCR gcse Gateway science physics, calculation of moving charge Q=It questions revision notes for OCR 21st Century science physics, calculation of moving charge Q=It questions revision notes WJEC GCSE physics, calculation of moving charge Q=It questions revision notes for CCEA gcse physics, calculation of moving charge Q=It questions revision notes for CIE Cambridge IGCSE physics exams. calculation of moving charge Q=It questions explained with examples, help in revising calculation of moving charge Q=It questions for gcse physics exams, knowing the importance of calculation of moving charge Q=It questions for gcse physics exams, key points to know about calculation of moving charge Q=It questions, exam revision notes for calculation of moving charge Q=It questions, Explaining the importance of how to calculate movement of charge Q in coulombs in GCSE level physics, What you need to know about how to calculate movement of charge Q in coulombs for GCSE level physics, Explaining what is the use of how to calculate movement of charge Q in coulombs knowledge in GCSE level physics, Examples of how to calculate movement of charge Q in coulombs explained when studying GCSE level physics, What is the significance of how to calculate movement of charge Q in coulombs in GCSE level physics, Describing and explaining the theory of how to calculate movement of charge Q in coulombs when studying GCSE level physics, revision notes for how to calculate movement of charge Q in coulombs in exams, online exam help for how to calculate movement of charge Q in coulombs, revision notes for how to calculate movement of charge Q in coulombs, what do I need to learn about how to calculate movement of charge Q in coulombs for by GCSE physics exam? revision summary for how to calculate movement of charge Q in coulombs, help in teaching how to calculate movement of charge Q in coulombs, learning notes for how to calculate movement of charge Q in coulombs, help to understand the how to calculate movement of charge Q in coulombs topic in preparation GCSE physics exam question, how to prepare for questions involving how to calculate movement of charge Q in coulombs in a GCSE physics examination?

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