Chapter 12: Electricity Revision Notes
Structure of the Atom
- The nucleus of an atom is positively charged, while the electrons that orbit it are negatively charged.
- Metals’ valence electrons are free to move around within the conductor, creating an electric current.
- Charge is a fundamental feature of matter that allows it to exert electromagnetic force.
Insulators and Conductors
- Conductors are substances that provide comparatively less resistance to the passage of electricity, whereas insulators provide more resistance.
Potential Difference and Electric Potential
- The effort done to move a unit positive charge from infinity to that location is defined as the electric potential at that place.
- The difference in electric potentials between two points is defined as the potential difference between two points.
MODELS OF ELECTRIC CURRENT
- Electric current (I = Q / t) is the flow of electric charges.
Electron sea model
- The drift of a ‘sea’ of free electrons, which are free to leap onto any nearby atom, causes electric current in a solid conductor.
Drift velocity of Electron
- The average velocity that an electron achieves inside a metallic conductor when an electric field is applied owing to a potential difference.
Battery and its working
- A cell is a source of potential difference that is generated internally by chemical processes.
- At anode: Cu(s)⇌Cu2+(aq)+2e−
- At cathode: Ag(aq)+2e−⇌2Ag(s)
- The term “battery” refers to a collection of cells.
- An electric circuit is a closed-loop channel that a current follows.
- A circuit diagram is a visual representation of an electric circuit using symbols.
OHM’S LAW AND RESISTANCE
- The applied potential difference between the two ends of an ohmic conductor is precisely proportional to the current flowing through it.
- A measure of the resistance to current flow in an electric circuit is called resistance.
Factors affecting Resistance & How they affect
The resistance of a conductor :
- is proportional to its length.
- directly proportionate to the conductor’s nature
- directly proportional to the temperature of the conductor.
- inversely proportional to the conductor’s cross-sectional area
- Resistivity is the electrical resistance provided by a material of unit length and cross-sectional area.
Ohmic and Non-Ohmic resistors
- Ohmic resistors are those that follow Ohm’s Law, whereas Non-Ohmic resistors are those that do not.
- Superconductors are conductors that have no resistance to the passage of electricity.
Combination of Resistors
- If two resistors carry the same current, they are said to be in series.
- When the same potential difference is applied to two resistors, they are said to be connected in parallel.
The equivalent resistance of two resistors can be calculated as follows:
In series, Req=R1+R2
In parallel, 1/Req= 1/R1+ 1/R2
Terminal Voltage and EMF
- When there is no current flowing through the circuit, the potential difference between the two terminals of a cell is called EMF.
- When current is flowing through a circuit, the potential difference between the two terminals of a cell is called terminal voltage.
Heating Effect of Current
- Heat (H) ∝ square of the current (I).
- H ∝ Resistance of the given circuit.
- H ∝ Time (t) for which current flows through the conductor.
- When a potential difference is generated, electrons travel, resulting in current flow.
- Electric power is the rate at which work is completed or electrical energy is used. If W is the amount of work completed in time t, then P=W/t.
- Watt is the SI unit (W). When 1 A of current flows at a potential difference of 1 V, one watt of electricity is consumed.
- A kilowatt-hour is a commercial unit of electrical energy (kWh).
- 3.6106J = 1 kWh = 3,600,000J
- P=I2R and P=V2/R are two symbols for the same thing.
- The amount of energy consumed when 1kW of electricity is used for 1 hour is defined as one kilowatt-hour.