Electric Current Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Electric Current.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

Electric current is the rate at which electric charge flows past a point in a circuit or conductor.

Current is like the flow rate of water in a pipe — how much charge passes a point each second.

Read the full concept explanation →

How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Electric Current asks students to follow the circuit path and identify what quantity changes at each component.

Common stuck point: Students often know a formula related to electric current but skip the recognition step: Can I identify the circuit path, what quantity is flowing or changing, and which electrical rule links the quantities? That leads to a correct-looking substitution attached to the wrong physical model.

Sense of Study hint: Ask: Can I identify the circuit path, what quantity is flowing or changing, and which electrical rule links the quantities?

Common Mistakes to Watch For

Before you work through the examples, skim the mistake guide so you know which shortcuts and sign errors to avoid.

Electric Current Mistakes

Worked Examples

Example 1

easy

A charge of

10 \text{ C}

flows through a wire in

5 \text{ s}

. What is the electric current?

Answer

I = 2 \text{ A}

First step

Use the current formula:

I = \frac{Q}{t}

Full solution

2
Substitute the given values: $I = \frac{10}{5}$ .
3
$I = 2 \text{ A}$

Electric current is the rate of flow of electric charge. One ampere means one coulomb of charge passes a point per second.

Example 2

medium

A current of

0.5 \text{ A}

flows through a lamp for

2 \text{ minutes}

. How much charge passes through the lamp?

Example 3

medium

A USB-C laptop charger delivers a steady

3.0\ \text{A}

for

45\ \text{minutes}

. How much charge flows through the cable?

Example 4

medium

A wire carries a steady current. In

10\ \text{s}

2.5\times10^{20}

electrons pass a cross-section. Find the current.

Example 5

hard

A pacemaker pulses

0.30\ \text{mA}

for

2.0\ \text{ms}

70

times per minute. How much total charge does it deliver in

1

minute?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

How long does it take for

15 \text{ C}

of charge to flow through a circuit with a current of

3 \text{ A}

Example 2

medium

A phone charger delivers a steady current of

2.0 \text{ A}

for

30 \text{ minutes}

. How much total electric charge flows through the cable?

Example 3

easy

What is the SI unit of electric current?

Example 4

easy

Write the formula relating current, charge, and time.

Example 5

easy

12

C flows past a point in

4

s, what is the current?

Example 6

easy

Does the same current that enters a resistor leave it, or is current 'used up'?

Example 7

easy

Convert

500

mA to amperes.

Example 8

easy

In which direction does conventional current flow relative to the battery terminals?

Example 9

easy

A current of

4

A flows for

5

s. How much charge passes?

Example 10

easy

Two points in a circuit pass

6

C and

6

C in the same second. Is the current the same at both?

Example 11

medium

A current starts at

0

and rises so that

24

C passes in

6

s. What is the average current?

Example 12

medium

A wire carries

0.2

A. How many coulombs pass in

1

minute?

Example 13

medium

A battery delivers

90

C over

30

s, then

30

C over the next

30

s. What is the average current over the full minute?

Example 14

medium

How many electrons per second pass a point carrying

1.6

Example 15

medium

A circuit needs

300

C delivered. The supply gives

0.25

A. How many minutes will it take?

Example 16

medium

A 5 A current flows through a wire. A student says the current is smaller after the bulb. Is this correct, and why?

Example 17

medium

At a junction,

7

A flows in and one branch carries

4

A out. What current leaves the other branch?

Example 18

challenge

A wire's current is

2

A for the first

10

s, then drops to

0.5

A for the next

20

s. What total charge flows, and what is the average current over

30

Example 19

challenge

A junction has three branches:

5

A enters,

2

A leaves one branch, and the third branch's direction is unknown. If the second branch is measured at

6

A leaving, what is the third branch current and direction?

Example 20

challenge

A device must transfer

4.8\times10^{20}

electrons in

2

minutes. What steady current does this require?

Example 21

medium

A current of

1.5

A flows for

40

s. How much charge passes?

Example 22

medium

A wire carries

0.4

A. How long to deliver

24

C of charge?

Example 23

easy

A wire carries

8\ \text{C}

past a point in

2\ \text{s}

. What is the current?

Example 24

easy

Convert

2.5\ \text{A}

to milliamperes.

Example 25

easy

Convert

750\ \text{mA}

to amperes.

Example 26

easy

A current of

3\ \text{A}

flows for

20\ \text{s}

. How much charge passes?

Example 27

easy

How long must

0.2\ \text{A}

flow to move

10\ \text{C}

of charge?

Example 28

medium

A junction has

9\ \text{A}

entering. Two branches leave: one carries

3\ \text{A}

, the other

5\ \text{A}

. What current does the third branch carry, and in what direction?

Example 29

medium

A wire carries

4\ \text{A}

for

5\ \text{minutes}

. How many electrons pass through?

Example 30

medium

A current rises linearly from

0

6\ \text{A}

4\ \text{s}

. What is the average current, and what total charge flows?

Example 31

medium

A circuit needs

5\ \text{C}

of charge delivered every

0.5\ \text{s}

steadily. What current is required?

Example 32

medium

A car battery delivers

50\ \text{A}

to a starter motor for

3\ \text{s}

. How much charge passes?

Example 33

medium

Two wires meet at a junction. Wire 1 has

7\ \text{A}

entering and wire 2 has

7\ \text{A}

leaving. What is the net current at the junction?

Example 34

medium

A current of

250\ \text{mA}

flows for

4\ \text{minutes}

. How much charge passes?

Example 35

hard

In a circuit,

4.0\ \text{A}

flows for

30\ \text{s}

, then

0\ \text{A}

for

30\ \text{s}

, then

2.0\ \text{A}

for

60\ \text{s}

. Find the average current over the full

2

minutes.

Example 36

hard

A junction has

4\ \text{A}

in from wire A and an unknown current

I_B

in from wire B. Two wires leave:

5\ \text{A}

and

6\ \text{A}

. Find

I_B

Example 37

hard

A device must transfer

9.6\times10^{19}

electrons in

80\ \text{ms}

. What current is required?

Example 38

hard

A circuit branch carries current

I(t) = 2t\ \text{A}

(with

t

in seconds) from

t=0

t=5\ \text{s}

. Find the total charge passing in that interval.

Example 39

hard

A single AA cell delivers

40\ \text{mA}

for

25\ \text{hours}

before dying. How much total charge did it provide?

Example 40

challenge

A circuit has three parallel branches sharing

12\ \text{A}

. Branch 1 carries twice the current of branch 2, and branch 3 carries the same as branch 2. Find each branch current.

Example 41

challenge

A copper wire of cross-section

1.0\ \text{mm}^2

carries

1.0\ \text{A}

. Given a free-electron density

n = 8.5\times10^{28}\ \text{m}^{-3}

, find the drift speed

v_d

of electrons. (Use

I = nAv_d e

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Related Concepts

Electric Charge Voltage Resistance Ohm's Law

Background Knowledge

These ideas may be useful before you work through the harder examples.

electric charge