Physics: Electricity, Circuits, and Electromagnetism

Electric Charge (Q)

The property of matter that causes it to experience a force when placed in an electric field

Coulombs (C)

unit of electric charge

Current (I)

The rate of flow of charge.

Amperes (A)

unit of current

Voltage (V)

The potential difference between two points; the work done to move a unit charge between those points.

Volts (V)

unit of voltage

​voltage

what formula is this for

V = Q/W

joule

one volt is equivalent to one ____ per coulomb.

Resistance (R)

The opposition to the flow of electric current.

Ohms (Ω)

unit of resistance

resistance

what formula is this for

R = V/I

Charge (Q)

The product of current (Ampere, A) and time

charge

What formula is this for

Q = I × t

Ohm's Law

The current through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant.

Ohm's Law

what formula is this for

V = IR

Electrical Power

The rate at which electrical energy is transferred by an electric circuit.

Watts (W)

unit of electrical power

electrical power

• Formulas:

  • P = IV

  • P = I²R

  • P = V²/R

energy transfer (Joule, J)

Formula: E = IVt 

power

The rate of energy transfer.

Watts (W)

unit for power

power

Formula: Energy transferred (J)/Time(s) ​

series circuits

• Characteristics

  • Current: Same through all components.

  • Voltage: Sum of voltages across components equals total voltage.

  • Resistance: Rₜₒₜₐₗ = R₁ + R₂ +…  

increased

If two resistors are in series, the net resistance is ________.

parallel circuits

• Characteristics

  • Current: Sum of currents through each path equals total current.

  • Voltage: Same across each component.

  • Resistance: 1/Rₜₒₜₐₗ = (1/R₁) + (1R₂) +... 

decreased

If two resistors are in parallel, the net resistance is ______

battery

Provides electrical energy.

resistor

Limits current flow

ammeter

Measures current (connected in series).

voltmeter

Measures voltage (connected in parallel).

switch

opens and closes the circuit.

closed circuit

A complete circuit where current can flow uninterrupted.

Kirchhoff's Current Law (KCL)

Total current entering a junction equals the total current leaving.

Kirchhoff's Voltage Law (KVL)

Total voltage around a closed loop equals zero.

Filament Lamps

The resistance increases as the temperature of the filament increases.

Diodes

Allow current to flow in one direction only, with very high resistance in the reverse direction

Fixed Resistors

Have a constant resistance regardless of the voltage and current

Light-Dependent Resistor (LDR)

Resistance decreases as light intensity increases.

Thermistors

Resistance decreases as temperature increases.

Magnetic Field Lines

Represent the direction and strength of the magnetic field. They flow from the north to the south pole of a magnet.

Magnetic Flux (Φ)

The total magnetic field passing through a given area.

Electromagnets

Magnets created by electric current flowing through coils of wire.

Electromagnets

Applications: Used in motors, generators, transformers, and relays.

Electromagnets

Construction: Typically a coil of wire (solenoid) with a ferromagnetic core.

The Motor Effect

A current-carrying conductor in a magnetic field experiences a force.

Fleming's Left-Hand Rule

Used to determine the direction of force on a current-carrying conductor

Thumb: Force (F)

First Finger: Magnetic Field (B)

Second Finger: Current (I)

Fleming's Left-Hand Rule:

• Thumb: ____

• First Finger: ______

• Second Finger: ______

Fleming's Left-Hand Rule

Formula: F = BIL

Faraday’s Law

Induced voltage in a circuit is proportional to the rate of change of magnetic flux through the circuit.

Lenz’s Law

The direction of the induced current opposes the change in magnetic flux.

Induced Voltage

Formula: ____________ = −dΦ/dt

Transformers

Devices that transfer electrical energy between two or more circuits through electromagnetic induction.

Transformers

Principle: Operates on AC; changing current in the primary coil induces a current in the secondary coil.

100%

Ideal transformers assume _______ efficiency (no energy loss).

Thermal Energy

Electrical energy is dissipated as __________ in the surroundings when an electric current does work against electrical resistance.

Reducing Unwanted Energy Transfer

Use low resistance wires to minimize energy loss.

Heating Effect of Current

• Advantages: Useful in devices like electric heaters and toasters.

• Disadvantages: Unwanted heating can damage components and reduce efficiency

Energy Transfer

Equation: E = IVt

Power

• Formula:

  • Power(W) = Energy transferred (J) ​/ Time(s)

  • P= IV

  • P = I²R 

Direct Current (DC)

Charge flows in one direction; supplied by cells and batteries

Alternating Current (AC)

Charge flow direction alternates; supplied by mains electricity

Live Wire

Carries current to the appliance.

Neutral Wire

Completes the circuit

Earth Wire

Safety wire to prevent electric shocks

• Live Wire

• Neutral Wire

• Earth Wire

WIRING TYPES

Fuses and Circuit Breakers

Protect circuits from excessive current.