TwiddleLab / Physics / Circuits You Can Build

Current: Charge on the Move

Lesson 2 of 10 · 7 min · Free, no account needed

What you will learn

• Current is how much charge passes a point each second: I = Q ÷ t.
• It is measured in amperes (A): 1 A is 1 coulomb (C) of charge every second.
• In a single loop the current is the same everywhere. A bulb takes energy from the charges, not the charges themselves.

Start the lesson

How the lesson goes

1. Does a bulb use up current, so less comes out than goes in?

   The meter before the bulb reads 0.5 A. Drag the marker to what the meter after it reads.

2. Clip the ammeter onto different places in the loop.

   Drag the meter onto any wire or part. Try at least three places.

3. What does 0.5 A actually count?

   A gate counts the charge that passes it. Press Play.

4. Charge on the move is called current.

   Current (I) is the charge that passes a point each second: I = Q ÷ t.

   Charge (Q) is counted in coulombs (C). Current is counted in amperes (A): 1 A = 1 C every second.

   In a single loop the current is the same everywhere. The bulb takes energy from the charges, never the charges.

5. Tap every meter that reads the same as the one marked 0.25 A.

   Two separate circuits share this board. Readings are hidden until you Check.

   Charge flows round a loop without piling up or disappearing, so every point of one loop carries the same current. A separate circuit has its own current.

6. Game: Meter detective. One meter on each board is broken. Tap it.

   Use what you know about loops. Fewest misses wins.

7. Code: computers store numbers as current on or off. Make the number 5.

   The bulbs are worth 8, 4, 2 and 1. Flip switches so the lit bulbs add up to 5.

   Each switch is a bit: current or no current, 1 or 0. Bits with place values 8, 4, 2, 1 can make every number from 0 to 15.

8. 6 C of charge pass a point in 3 s. What is the current?

   I = Q ÷ t = 6 C ÷ 3 s = 2 C/s = 2 A.

9. Your bet from the start against the real meter.

Previous lesson: Close the Loop · Next lesson: Voltage: The Push Behind the Flow · Part of the course: Circuits You Can Build

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