electric current and electric power.

Physics Notes: Electric Current & Electric Power

1. Electric Current

Definition

Electric current is the flow of electric charge (electrons) through a conductor.

• Symbol: I

• Unit: Ampere (A)

1 ampere (A) = 1 coulomb of charge per second

[
1A = \frac{1C}{1s}
]

2. Conductors

A conductor is a material that allows electrons to move freely.

Examples:

• Copper

• Gold

• Iron

• Steel

This ability is called conductivity.

3. Electron Movement

• Electrons have a negative charge.

• Like charges repel each other.

• When electrons are pushed through a wire, they form an electric current.

Unlike static electricity, electric current involves continuous movement of electrons.

4. Electric Circuit

An electric circuit is a closed path that allows electrons to flow.

A circuit needs:

• Battery (energy source)

• Conducting wires

• Device (light bulb, motor, etc.)

• Complete loop

If the circuit is open (broken wire), no current flows.

5. Battery

A battery has two terminals:

• Negative (−): Electrons leave here.

• Positive (+): Electrons move toward here.

The battery uses a chemical reaction to create a difference in electric potential (voltage).

6. Voltage

Definition

Voltage is the electric potential energy per unit charge.

• Symbol: V

• Unit: Volt (V)

[
1V = 1\frac{J}{C}
]

Meaning:

• 1 volt = 1 joule of energy per coulomb of charge

Higher voltage → More energy available to move electrons.

Electric Power

Definition

Electric power is the rate at which electrical energy is transferred or used.

• Symbol: P

• Unit: Watt (W)

[
1W = 1\frac{J}{s}
]

Meaning:

• 1 watt = 1 joule of energy used every second

Power Formula

[
\boxed{P = V \times I}
]

Where:

• P = Power (watts, W)

• V = Voltage (volts, V)

• I = Current (amps, A)

Rearranged Formulas

To find current:

[
\boxed{I=\frac{P}{V}}
]

To find voltage:

[
\boxed{V=\frac{P}{I}}
]

Unit Relationships

Voltage:

[
V=\frac{J}{C}
]

Current:

[
A=\frac{C}{s}
]

Power:

[
W=\frac{J}{s}
]

Notice:

[
\left(\frac{J}{C}\right)\left(\frac{C}{s}\right)=\frac{J}{s}
]

The coulombs cancel, leaving watts.

Example 1: Nuclear Power Plant

Given

Voltage:

[
V=6.2\times10^5V
]

Current:

[
I=30.0A
]

Formula:

[
P=VI
]

Calculation:

[
P=(6.2\times10^5)(30.0)
]

[
P=1.9\times10^7W
]

Convert to megawatts:

[
1MW=10^6W
]

[
P=19MW
]

Answer: 19 megawatts

Example 2: Alarm Clock

Given

Power:

[
P=4.0W
]

Voltage:

[
V=120V
]

Formula:

[
I=\frac{P}{V}
]

Calculation:

[
I=\frac{4.0}{120}
]

[
I=0.033A
]

Scientific notation:

[
\boxed{I=3.3\times10^{-2}A}
]

Answer: 3.3 × 10⁻² amps

Example 3: Light Bulb

Given

Voltage:

[
V=9.0V
]

Current:

[
I=0.9A
]

Formula:

[
P=VI
]

Calculation:

[
P=9.0\times0.9
]

[
\boxed{P=8.1W}
]

An 8.1-watt bulb produces much less light than:

• 60 W incandescent bulb

• 14 W compact fluorescent bulb

Scientific Notation Review

[
3.3\times10^{-2}=0.033
]

[
1.9\times10^7=19,000,000
]

Key Vocabulary

Essential Formulas

[
\boxed{P=VI}
]

[
\boxed{I=\frac{P}{V}}
]

[
\boxed{V=\frac{P}{I}}
]

[
\boxed{1V=\frac{J}{C}}
]

[
\boxed{1A=\frac{C}{s}}
]

[
\boxed{1W=\frac{J}{s}}
]

Summary

• Electric current is the movement of electrons through a conductor.

• A closed circuit is required for current to flow.

• Batteries create voltage, which pushes electrons through the circuit.

• Voltage measures energy per unit charge.

• Electric power measures how quickly electrical energy is used.

• The most important equation is:

[
\boxed{P=VI}
]

• Current can be found using:

[
\boxed{I=\frac{P}{V}}
]

• Voltage can be found using:

[
\boxed{V=\frac{P}{I}}
]

• Example: A 4.0 W alarm clock connected to a 120 V outlet draws:

[
\boxed{I=3.3\times10^{-2}\text{ A}}
]