A-level Physics (Advancing Physics)/Current

Current is the amount of charge (on particles such as electrons) flowing through part of an electric circuit per second. Current is measured in amps (usually abbreviated A), where 1 amp equals 1 coulomb of charge per. second. The formula for current is:

$I=\frac{\mathrm{\Delta }Q}{\mathrm{\Delta }t}$ (What's that weird triangle thing?)

i₁ + i₄ = i₂ + i₃

where I = current (A), Q = charge (C) and t = time (seconds).

In a series circuit, the current is the same everywhere in the circuit, as the rate of flow of charged particles is constant throughout the circuit. In a parallel circuit, however, the current is split between the branches of the circuit, as the number of charged particles flowing cannot change. This is Kirchoff's First Law, stating that:

In mathematical form:

$\sum I_{in}=\sum I_{out}$ (What's that distorted 'E'?)

Questions

1. 10 coulombs flow past a point in a wire in 1 minute. How much current is flowing through the point?

2. How long does it take for a 2A current to carry 5C?

3. In the diagram on the left, I = 9A, and I₁ = 4.5A. What is the current at I₂?

4. What would I equal if I₁ = 10A and I₂ = 15A?

5. In the diagram on the left, in 5 seconds, 5C of charged particles flow past I₁, and 6.7C flow past I₂. How long does it take for 10C to flow past I?

/Worked Solutions/