Current

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Lesson notes

What is Current?

**Current** is the flow of charge through a circuit.
It is equal to how much charge flows past a point every second.
The charged particles that flow are **electrons** (negatively charged).
A **complete circuit** is needed for current to flow.

Measuring Current

Current is measured in **amps (A)**.
An **ammeter** measures current at a point in the circuit.
The circuit symbol for an ammeter is a circle with an “A” inside.

Series Circuits

A **series circuit** has only one path for current.
Current is **the same everywhere** in a series circuit.
Example: a series circuit with one lamp has 2 A at every point.

Parallel Circuits

A **parallel circuit** has more than one path for current.
At a **junction**, total current in equals total current out.
Each branch draws current from the cell; total current is the sum of branch currents.
Higher **resistance** in a path means **lower current** in that path.

Current and Resistance

Resistance opposes current flow.
In a parallel circuit with identical lamps, each branch has the same current.
If one path has more lamps (more resistance), its current is less.
Overall current from the battery is the sum of the branch currents.

A series circuit with a cell, switch, lamp, and ammeter. Current is the same at all points.

In a series circuit, the ammeter readings are equal (2 A everywhere).

Slides

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Practice questions

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1.What is the unit of electric current?
Easy
- AAmps
- BVolts
- COhms
- DWatts
2.Which instrument is used to measure electric current?
Easy
- AVoltmeter
- BAmmeter
- COhmmeter
- DGalvanometer
3.What particles flow through a circuit to create an electric current?
Easy
- AProtons
- BNeutrons
- CElectrons
- DIons
4.In a series circuit, the current is:
Easy
- Adifferent at different points
- Bthe same everywhere
- Chigher near the battery
- Dlower near the bulb
5.In a parallel circuit, the total current entering a junction is equal to:
Medium
- Athe current in the smallest branch
- Bthe average of the branch currents
- Cthe total current leaving the junction
- Dthe current in the largest branch
6.A series circuit has a 2 A current. What is the current after passing through a lamp?
Medium
- A0 A
- B1 A
- C2 A
- D4 A
7.In a parallel circuit with two identical lamps, the current in each branch is 2 A. What is the total current drawn from the battery?
Medium
- A2 A
- B4 A
- C1 A
- D0 A
8.In a parallel circuit, one branch has a single lamp and the other branch has two identical lamps in series. The current through the single lamp is 2 A. What is the current through each of the two lamps?
Hard
- A2 A each
- B1 A each
- C0.5 A each
- D4 A each

Revision notes

## Current in Circuits - **Current** is the flow of charge (electrons) past a point per second. Measured in **amps (A)** using an **ammeter** (symbol: circle with 'A'). - A **complete circuit** is needed for current to flow. - **Series circuit**: only one path; current is **the same everywhere**. - **Parallel circuit**: multiple paths; at a junction, **total current in = total current out**. Each branch draws additional current from the cell. - **Resistance** affects current: higher resistance → lower current. ### Key Rules - In series: \( I_{total} = I_1 = I_2 = ... \) - In parallel: \( I_{total} = I_1 + I_2 + ... \) (current splits at junctions) ### Example (from source) - Identical lamps: each branch gets same current (e.g., 2 A). Before/after junction, total current is sum (e.g., 4 A). - If one branch has more lamps (higher resistance), its current is lower (e.g., 2 A vs 1 A). Total drawn from battery = sum of branch currents (e.g., 3 A).

Current: The rate of flow of charge past a point in a circuit, measured in amps (A).
Ammeter: A device used to measure current, connected in series. Symbol: circle with 'A'.
Electron: A negatively charged particle that flows through a circuit.
Series circuit: A circuit with only one path for current; current is the same at all points.
Parallel circuit: A circuit with more than one path for current; total current into a junction equals total current out.
Junction: A point in a circuit where wires split or combine.
Resistance: A property that opposes current flow; higher resistance reduces current.

Flashcards

What is electric current?

Current is the flow of charge past a point in a circuit every second.

What is the unit of current?

Amps (A).

What instrument measures current?

An ammeter.

What is the circuit symbol for an ammeter?

A circle with an 'A' inside.

What charged particles flow through a circuit?

Electrons, which are negatively charged.

What is needed for current to flow?

A complete circuit.

In a series circuit, how does current compare at different points?

Current is the same everywhere in a series circuit.

How many paths for current are there in a series circuit?

Only one path.

In a parallel circuit, what is the rule for current at a junction?

The total current going into a junction equals the total current going out.

How does resistance affect current in a path?

Higher resistance leads to lower current.

In a parallel circuit with identical lamps, how does current in each branch compare?

Each branch has the same current if the lamps are identical.

If a parallel circuit has two identical branches each with 2 A, what is the total current before the junction?

4 A.

In a series circuit with one lamp, if current is 2 A at one point, what is it at another point?

2 A, because current is the same everywhere.

What happens to current when you add more lamps in series?

Current decreases because total resistance increases.

In a parallel circuit, if one branch has two lamps and another has one lamp (identical lamps), which branch has higher current?

The branch with one lamp has higher current because it has lower resistance.

True or False: Current is equal to how much charge flows past a point per second.

True.

True or False: Protons flow through a circuit.

False. Electrons flow.

True or False: Current can flow through an incomplete circuit.

False. A complete circuit is needed.

True or False: In a series circuit, current is different at different points.

False. Current is the same everywhere.

What is the circuit symbol for a cell?

Two parallel lines, one longer (positive) and one shorter (negative).

What is the circuit symbol for a lamp?

A circle with a cross inside.

In a parallel circuit with two branches, one with 2 A and one with 1 A, what is the total current from the battery?

3 A.

How does adding more lamps in parallel affect the total current drawn from the battery?

It increases because each branch adds more current.

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