Standard X Physics Part 1: Electrical Energy

Standard X Physics Part 1 Notes

• This book talks about Physics for Standard X students and is part 1 in a series
• It is created by the Government of Kerala, Department of General Education
• It is written by the State Council of Educational Research and Training (SCERT) Kerala, 2019

Key Concepts

• Electrical energy can be transformed into different forms
• A device’s impact of electric current turns electrical energy into a useful form
• According to the law of conservation of energy, energy can neither be created nor destroyed

Heating Effect of Electric Current

• These devices give heating effect of electric current, such as Electric iron
• Required Material: Nichrome wire of approximate length 5 cm, 6 V storage battery, and Connection wires
• The voltage between the ends of the resistor R (nichrome wire) can be measured using a voltmeter V, and the current through it can be measured using an ammeter A. Potential difference between two points will be one volt if one joule of work is done in moving one coulomb of charge from one point to the other

Formulas to remember

• Current I = Q/t
• The charge that flows through the conductor in t seconds, Q=coulomb
• The work W to be done to move one coulomb of charge under a potential difference V will be, W = V joule
• The power P supplied by the battery to the circuit in a time t seconds is P = W/t
• Electrical energy expended by the battery containing the nichrome wire and converted into heat: H = VIt
• With Ohm's Law (V=IR): H=VIt = I2Rt

Joule's Law

• The heat generated (H) in a current carrying conductor is directly proportional to the product of the square of the current (I) in the conductor, the resistance of the conductor (R) and the time (t) of flow of current
• H ∞ I²Rt --> H = I2Rt joule
• I is the current in ampere, R is the resistance in ohm, and t is the time in seconds

Resistors in Series

• When resistors are connected in series, the effective resistance increases
• The potential difference gets divided such that V = V₁ +V₂
• V₁ = IR₁, and V₂ = IR₂
• Voltage across the higher resistance is greater

Resistors in Parallel

• The current completes the circuit by getting divided into each branch
• The total current equals I = I₁ + I₂
• The formula is: 1/R = 1/R₁ + 1/R₂
• The formula by Ohm's Law is: V/R=V/R₁ +V/R₂

Heating Effect of Electricity

• Electric heating appliances are instruments that make use of the heating effect of electricity
• Electrical energy is converted into heat energy

Safety Fuse

• The safety fuse is a device that works on the heating effect of electric current
• Fuse wire, an alloy of tin and lead, has a relatively low melting point
• Joule's Law states that more heat will be produced when electric current increases
• Once heat is generated, the Fuse wire melts and the circuit is broken

Electric Power

• The amount of energy consumed by an electrical appliance is its power
• The formula to calculate electrical power is P=W/t
• Unit of electric power is watt (W)

Lighting Effect of Electric Current

• Incandescent lamps with filaments made of metal tungsten are used to radiate out light
• When tungsten becomes hot and emits white light for a long time, in order to avoid oxidation of tungsten, the bulb is evacuated
• Vaporization can be reduced by filling some inert gas at low pressure inside the bulb, which is usually nitrogen
• Nitrogen behaves like an inert gas at normal temperature and pressure
• High resistivity, melting point, ductility, and emitting white light makes tungsten a suitable filament

LED Bulbs

• LEDs, or Light Emitting Diodes, give more light than discharge lamps and incandescent lamps using low power
• There's no energy lost in heat form because it doesn't have a filament
• LEDs are not harmful to the environment because they do not contain mercury

Electromagnetism

• Hans Christian Oersted noticed a magnetic needle experinced deflectino near a current carrying conductor, discovering electromagnetic
• The magnetic field lines of the bar magnet and of the electromagnets are similar
• The magnetic strength/magnetism of an electromagnet is temporary
• Right Hand Thumb Rule of James Clark Maxwell: if the conductor is held with your right hand, the thumb pointing in the direction of the current, then the direction in which the other fingers encircle the conductor gives the direction of the magnetic field.
• Right Hand Screw Rule: If a right hand screw is rotated so that its tip advances along the direction of the current in the conductor, then the direction of rotation of the screw gives the direction of the magnetic field around the conductor

Electric Motor

• Armature is metallic coil wound round a soft iron core, fixed firmly on the axis XY
• If the rotation of the armature is to be sustained the direction of current through the armature should continuously rotate
• Split rings help change the direction of current through the coil after every half rotation

Electromagnetic induction

Mutual Induction

• Magnetic flux is formed around soft iron core when current is passed