Forms and Sources of Energy

• Energy is the ability to do work, and all living things need energy to do work.
• The S.I. unit for energy is the joule.

Forms of energy

• Energy cannot be created or destroyed in various forms
• The forms of energy include sound, kinetic, electrical, light, nuclear, heat, chemical, elastic potential, and gravitational potential energy.

Sources of Energy

• Sources of energy include the Sun, wind, water, biomass, geothermal, wave, fossil fuels, and radioactive substances.

Electrostatic Charges

• Electrostatic charges are electric charges that are not free to move, consisting of positive (protons) and negative (electrons).
• Electrostatic charges are produced when objects of different types are rubbed together.
• During the generation of electrostatic charges, electrons are transferred from one object to another, while protons do not move.
• An object that gains electrons becomes negatively charged and has more electrons than protons.
• An object that loses electrons becomes positively charged and has more protons than electrons.

Electrostatic Forces

• Electrostatic charges interacting with each other produce an electrostatic force.
• Like charges produce a repulsive force.
• Opposite charges produce an attractive force.

Effect of production of electrostatic charges

• When a plastic comb is rubbed with a woolen cloth, the comb gains electrons from the cloth and becomes negatively charged.
• The negatively charged comb can then attract pieces of paper due to the attraction force between the positive charges in the paper and the negative charges on the comb.

Electroscope

• An electroscope is a device used to detect the existence of electric charges on an object.
• If a neutral strip is brought close to an electroscope and the gold leaf does not diverge, it indicates that the positive and negative charges are attracted to one another.
• If a neutral strip is brought close and the gold leaf diverges, it indicates that the same charges repel each other (either positively or negatively charged).

Examples of Electrostatic in Our Daily Life

• The friction between clouds and air causes clouds to become charged with electric charges, which can lead to lightning.
• Negative charges in the clouds are attracted to positive charges on the earth's surface, resulting in lightning.
• Lightning conductors are installed on buildings to provide a path for electric charges to flow into the ground, protecting the building from lightning strikes.
• Computer screens quickly become dusty because the negative charge on the dust is attracted to the positive charge on the screen.
• Anti-static cloths (microfiber cloths) are used to transfer charges on the screen, and anti-static films can be applied to the screen.

Electric Current

• Electric current is produced by electrons (negative charges) flowing in electrical conductors.
• A Galvanometer's pointer indicates the flow of electric current.

Current

• Current is the rate of flow of electric charges (electrons) through a conductor.
• The flow of electric current can be measured using an ammeter.
• The S.I. unit for current is the ampere (A).

Voltage

• Voltage is the potential difference between two points.
• Voltage can be measured using a voltmeter.
• The S.I. unit for voltage is the volt (V).

Resistance

• Resistance is the ability of a conductor to limit or resist the flow of electric current.
• A resistor is an electrical component that has resistance.
• The S.I. unit for resistance is the ohm (Ω).

The Relationship between Current, Voltage and Resistance

• Current, voltage, and resistance are closely related in a circuit, and changes in one affect the others.
• The relationship between the current (I), the voltage (V), and the resistance (R) is described by Ohm's Law.
• The electric current (I) that flows through a conductor is directly proportional to the voltage (V) across it if the resistance (R) is constant.
• The Ohm's Law is obeyed if the temperature and physical condition of the conductor used is constant.
• When a higher voltage flows through the circuit, the amount of current flowing through the circuit also increases.

Ohm's Law Triangle

• Ohm's Law triangle can help solve questions easier.
• Draw the triangle first during the exam.
• If the question gives I and R and asks you to find V, then cover V with your finger and you will know that V = IR. The same goes for finding other ones. The same (if you want to find R. cover R and you will know R = V ÷ I).

Electrical Circuit Components

• Switch, Resistor, Voltmeter, Variable Resistor, Ammeter, Dry Cell, Galvanometer, Bulb, Fuse

Series Circuit

• Electrical components are connected one after another in a single path
• The current is the same through each component (I = I1 = I2 = I3)
• The total voltage is the sum of the voltages across each component (V = V1 + V2 + V3)
• The total resistance is the sum of the individual resistances (R = R1 + R2 + R3)
• Every component in the circuit receives the same amount of current.
• Every component is controlled by the same switch.
• An increase in voltage supplies more electric current.
• If one of the electrical appliances is damaged, other electrical appliances cease to function.
• Adding more electrical appliances increases resistance and decreases the flow of the current.
• Each electrical appliance cannot be switched off individually.

Parallel Circuit

• Electrical components are separated into several different paths of the electrical circuit.
• Each parallel path has electrical components.
• The total current is the sum of the currents through each component (I =I1 + I2 + I3)
• The voltage is the same across each component (V = V1 = V2 = V3)
• Every electrical appliance can be switched on or off separately.
• The increase in the number of electrical appliances does not affect the function of other appliances in the same circuit.
• The voltage for every electrical appliance cannot be adjusted because the voltage is the same as the source of voltage.
• The electrical wiring system in our homes is connected in parallel to ensure every light gets the same voltage from its main power supply.
• The distribution panel controlled the current that flows from the main power supply to the circuit.

Magnets

• Magnets exist naturally in the form of lodestones and are also man-made.

Properties of a Magnet

• Attracts magnetic materials.
• Has two poles (north and south pole).
• Produces a magnetic field and magnetic force.
• A freely suspended magnet aligns in a north-south direction.
• Like poles repel, unlike poles attract.

Magnetic Field

• The area around a magnet with magnetic force.

Characteristics of magnetic field lines

• Magnetic field lines begin from the north pole and end at the south pole.
• Magnetic field lines never meet or cross.
• Magnetic field lines are closer together where the magnetic field is stronger.
• A magnetic field between two like poles will produce a neutral region where the magnetic field is weak.

Electromagnet

• An electromagnet is a magnet formed from an electrical conductor carrying an electric current.
• Electromagnets are temporary magnets (disappear when the electric current is cut off)

The pattern and direction of the magnetic field

• Depends on the shape of the conductor used.
• The magnetic field lines produced by a straight wire and a coiled wire are concentric circles.
• The strength of the magnetic field reduces as it moves away from the center of the conductor.
• Depends on the direction of the electric current.
• The right-hand grip rule determines the magnetic field direction of the current flow in a straight wire.

Factors that influence the strength of the magnetic field

• Current flow: the larger the current, the stronger the magnetic field.
• The number of turns of a coil (solenoid): the more turns, the stronger the magnetic field.

Application of Magnets and Electromagnets in Daily Life

• The needle of a compass uses a magnet to show direction.
• Credit and debit cards have an electromagnetic strip that stores information.
• Magnetic locks use electromagnets to lock doors automatically.