Physics: Electricity, Circuits, and Electromagnetism

**Electricity**

**1.1 Electrical Quantities**

**Electric Charge (Q)**The property of matter that causes it to experience a force when placed in an electric field.

Unit:

**Coulombs (C)**Example: A charge of 1 C is equal to the charge of approximately

electrons.*6.242×10¹⁸*

**Current (I)**Definition: The rate of flow of charge.

Unit:

**Amperes (A)**Formula:

*I = Q/t*Example: A current of 2 A means 2 C of charge passes a point in the circuit every second.

In metals, current is the flow of electrons.

**Voltage (V)****The potential difference between two points; the work done to move a unit charge between those points.****Unit: Volts (V)****Formula:***V = W/Q*Potential difference (voltage) is the energy transferred per unit charge passed. Thus, one volt is equivalent to one joule per coulomb.

**Example: A battery that provides 9 V does 9 joules of work per coulomb of charge.**

**Resistance (R)****The opposition to the flow of electric current.****Unit: Ohms (Ω)****Formula:***R = V/I***Example: If a resistor has a voltage of 10 V across it and a current of 2 A flowing through it, its resistance is 5 Ω.****Changing Resistance: Using a variable resistor in a circuit can change the resistance, thereby changing the current.**

**Charge (Q)****Formula:***Q = I × t***Explanation: Charge (Coulomb, C) is the product of current (Ampere, A) and time (second, s).**

**1.2 Ohm's Law**

**Statement**: The current through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant.**Formula**:*V = IR***Graph**: A linear graph showing direct proportionality between current and voltage for a conductor obeying Ohm’s law.

**1.3 Electrical Power**

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

**Unit**:**Watts (W)****Formulas**:*P = IV**P = I²R**P = V²/R*

**Example**: A 60 W light bulb uses 60 joules of energy per second.

**1.4 Energy Transfer**

**Formula**:*E = IVt***Explanation**: Energy transferred (Joule, J) is the product of current (Ampere, A), potential difference (Volt, V), and time (second, s).

**1.5 Power**

**Definition**: The rate of energy transfer.**Unit**: Watts (W)**Formula**:*Power(W) = Energy transferred (J)/Time(s)*

**Circuits**

**2.1 Series and Parallel Circuits**

**Series Circuits**

**Characteristics****Current: Same through all components.****Voltage: Sum of voltages across components equals total voltage.****Resistance:***Rₜₒₜₐₗ = R₁ + R₂ +…***Explanation: If two resistors are in series, the net resistance is increased.**

Example: Christmas lights where one bulb failure affects the entire string.

**Parallel Circuits**

**Characteristics****Current: Sum of currents through each path equals total current.****Voltage: Same across each component.****Resistance:***1/Rₜₒₜₐₗ = (1/R₁) + (1R₂) +...***Explanation: If two resistors are in parallel, the net resistance is decreased.****Example: Household electrical wiring.**

**2.2 Circuit Components**

**Symbols and Functions****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.

**2.3 Kirchhoff's Laws**

**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.

**2.4 Device Behavior in Circuits**

**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.

**2.5 Variable Resistances**

**Light-Dependent Resistor (LDR)**: Resistance decreases as light intensity increases.**Thermistors**: Resistance decreases as temperature increases.**Exploring Variation**: Use of circuits to investigate how resistance changes in filament lamps, diodes, thermistors, and LDRs.

**Electromagnetism**

**3.1 Magnetic Fields**

**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.

**3.2 Electromagnets**

**Definition**: Magnets created by electric current flowing through coils of wire.**Applications**: Used in motors, generators, transformers, and relays.**Construction**: Typically a coil of wire (solenoid) with a ferromagnetic core.

**3.3 The Motor Effect**

**Definition**: 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)**Formula**:*F = BIL***Example**: Electric motors use this effect to produce motion.

**3.4 Electromagnetic Induction**

**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.**Formula**:*Induced Voltage = −dΦ/dt***Applications**: Transformers and electric generators operate based on this principle.

**3.5 Transformers**

**Definition**: Devices that transfer electrical energy between two or more circuits through electromagnetic induction.**Principle**: Operates on AC; changing current in the primary coil induces a current in the secondary coil.**Formula**:*VₚVₛ = NₚNₛ***Efficiency**: Ideal transformers assume 100% efficiency (no energy loss).

**Electrical Energy and Safety**

**4.1 Energy Dissipation**

**Thermal Energy**: Electrical energy is dissipated as thermal energy in the surroundings when an electric current does work against electrical resistance.**Reducing Unwanted Energy Transfer**: Use low resistance wires to minimize energy loss.

**4.2 Heating Effect of Current**

**Advantages**: Useful in devices like electric heaters and toasters.**Disadvantages**: Unwanted heating can damage components and reduce efficiency.

**4.3 Power and Energy Transfer**

**Equation**:*E = IVt***Power Formula**:*Power(W) = Energy transferred (J) / Time(s)**P= IV**P = I²R*

**4.4 Domestic Electrical Systems**

**Energy Transfer**: Batteries and the a.c. mains supply energy to motors and heating devices.**Direct vs Alternating Voltage**:**Direct Current (DC)**: Charge flows in one direction; supplied by cells and batteries.**Alternating Current (AC)**: Charge flow direction alternates; supplied by mains electricity.

**Wiring**:**Live Wire**: Carries current to the appliance.**Neutral Wire**: Completes the circuit.**Earth Wire**: Safety wire to prevent electric shocks

**Safety**:**Fuses and Circuit Breakers**: Protect circuits from excessive current.Switches and Fuses Location

# Physics: Electricity, Circuits, and Electromagnetism

**Electricity**

**1.1 Electrical Quantities**

**Electric Charge (Q)**The property of matter that causes it to experience a force when placed in an electric field.

Unit:

**Coulombs (C)**Example: A charge of 1 C is equal to the charge of approximately

electrons.*6.242×10¹⁸*

**Current (I)**Definition: The rate of flow of charge.

Unit:

**Amperes (A)**Formula:

*I = Q/t*Example: A current of 2 A means 2 C of charge passes a point in the circuit every second.

In metals, current is the flow of electrons.

**Voltage (V)****The potential difference between two points; the work done to move a unit charge between those points.****Unit: Volts (V)****Formula:***V = W/Q*Potential difference (voltage) is the energy transferred per unit charge passed. Thus, one volt is equivalent to one joule per coulomb.

**Example: A battery that provides 9 V does 9 joules of work per coulomb of charge.**

**Resistance (R)****The opposition to the flow of electric current.****Unit: Ohms (Ω)****Formula:***R = V/I***Example: If a resistor has a voltage of 10 V across it and a current of 2 A flowing through it, its resistance is 5 Ω.****Changing Resistance: Using a variable resistor in a circuit can change the resistance, thereby changing the current.**

**Charge (Q)****Formula:***Q = I × t***Explanation: Charge (Coulomb, C) is the product of current (Ampere, A) and time (second, s).**

**1.2 Ohm's Law**

**Statement**: The current through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant.**Formula**:*V = IR***Graph**: A linear graph showing direct proportionality between current and voltage for a conductor obeying Ohm’s law.

**1.3 Electrical Power**

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

**Unit**:**Watts (W)****Formulas**:*P = IV**P = I²R**P = V²/R*

**Example**: A 60 W light bulb uses 60 joules of energy per second.

**1.4 Energy Transfer**

**Formula**:*E = IVt***Explanation**: Energy transferred (Joule, J) is the product of current (Ampere, A), potential difference (Volt, V), and time (second, s).

**1.5 Power**

**Definition**: The rate of energy transfer.**Unit**: Watts (W)**Formula**:*Power(W) = Energy transferred (J)/Time(s)*

**Circuits**

**2.1 Series and Parallel Circuits**

**Series Circuits**

**Characteristics****Current: Same through all components.****Voltage: Sum of voltages across components equals total voltage.****Resistance:***Rₜₒₜₐₗ = R₁ + R₂ +…***Explanation: If two resistors are in series, the net resistance is increased.**

Example: Christmas lights where one bulb failure affects the entire string.

**Parallel Circuits**

**Characteristics****Current: Sum of currents through each path equals total current.****Voltage: Same across each component.****Resistance:***1/Rₜₒₜₐₗ = (1/R₁) + (1R₂) +...***Explanation: If two resistors are in parallel, the net resistance is decreased.****Example: Household electrical wiring.**

**2.2 Circuit Components**

**Symbols and Functions****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.

**2.3 Kirchhoff's Laws**

**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.

**2.4 Device Behavior in Circuits**

**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.

**2.5 Variable Resistances**

**Light-Dependent Resistor (LDR)**: Resistance decreases as light intensity increases.**Thermistors**: Resistance decreases as temperature increases.**Exploring Variation**: Use of circuits to investigate how resistance changes in filament lamps, diodes, thermistors, and LDRs.

**Electromagnetism**

**3.1 Magnetic Fields**

**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.

**3.2 Electromagnets**

**Definition**: Magnets created by electric current flowing through coils of wire.**Applications**: Used in motors, generators, transformers, and relays.**Construction**: Typically a coil of wire (solenoid) with a ferromagnetic core.

**3.3 The Motor Effect**

**Definition**: 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)**Formula**:*F = BIL***Example**: Electric motors use this effect to produce motion.

**3.4 Electromagnetic Induction**

**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.**Formula**:*Induced Voltage = −dΦ/dt***Applications**: Transformers and electric generators operate based on this principle.

**3.5 Transformers**

**Definition**: Devices that transfer electrical energy between two or more circuits through electromagnetic induction.**Principle**: Operates on AC; changing current in the primary coil induces a current in the secondary coil.**Formula**:*VₚVₛ = NₚNₛ***Efficiency**: Ideal transformers assume 100% efficiency (no energy loss).

**Electrical Energy and Safety**

**4.1 Energy Dissipation**

**Thermal Energy**: Electrical energy is dissipated as thermal energy in the surroundings when an electric current does work against electrical resistance.**Reducing Unwanted Energy Transfer**: Use low resistance wires to minimize energy loss.

**4.2 Heating Effect of Current**

**Advantages**: Useful in devices like electric heaters and toasters.**Disadvantages**: Unwanted heating can damage components and reduce efficiency.

**4.3 Power and Energy Transfer**

**Equation**:*E = IVt***Power Formula**:*Power(W) = Energy transferred (J) / Time(s)**P= IV**P = I²R*

**4.4 Domestic Electrical Systems**

**Energy Transfer**: Batteries and the a.c. mains supply energy to motors and heating devices.**Direct vs Alternating Voltage**:**Direct Current (DC)**: Charge flows in one direction; supplied by cells and batteries.**Alternating Current (AC)**: Charge flow direction alternates; supplied by mains electricity.

**Wiring**:**Live Wire**: Carries current to the appliance.**Neutral Wire**: Completes the circuit.**Earth Wire**: Safety wire to prevent electric shocks

**Safety**:**Fuses and Circuit Breakers**: Protect circuits from excessive current.Switches and Fuses Location