Atomic Structure
- An atom has a positively charged nucleus and negatively charged electrons revolving around it.
- Valence electrons in metals are free to move within the conductor and constitute an electric current.
Charge
The charge is an intrinsic property of matter by virtue of which it can exert electromagnetic force.
Conductors and Insulators
A substance that offers comparatively less opposition to the flow of current is known as a conductor and substances which offer larger opposition are insulators.
Some examples of conductors include copper, iron, and steel. Some examples of insulators include glass, dry wood, and cotton.
Electric Potential and Potential Difference
The electric potential at a point is defined as work done in bringing a unit positive charge from infinity to that point. The potential difference between two points is defined as the difference in electric potentials at the two given points. The electrons move only if there is a difference in electric pressure called the potential difference. One Volt is defined as energy consumption of one joule per electric charge of one coulomb.
Mathematically, the electric potential between two points is given as:
where V is the potential difference, W is the work done, and Q is the electric charge.
Electric Current(I)
The flow of electric charges is called an electric current, i.e, I = Q / t
Models of Electric Current
Drift velocity of Electron
Average velocity which an electron attains inside a metallic conductor due to the application of an electric field due to the potential difference.
Battery and its working
A cell is a source of potential difference, which is created inside it due to internal chemical reactions.
At anode: Cu(s)⇌Cu2+(aq)+2e−
At cathode: Ag(aq)+2e−⇌2Ag(s)
A combination of cells is called a battery.
Anatomy of a Battery
Electric Circuit
Electric circuit and circuit diagram
- A closed-loop path that a current take is called an electric circuit.
- The representation of an electric circuit through symbols is called a circuit diagram.
Resistance and Ohm’s Law
Ohm’s law
The current flowing through an ohmic conductor is directly proportional to the applied potential difference between the two ends of the conductor. Ohm’s Law states the relationship between the potential difference across a conductor and the current through it
Factors affecting Resistance & How they affect
Resistance is:
- directly proportional to the length of the conductor.
- directly proportional to nature of the conductor.
- directly proportional to the temperature of the conductor.
- inversely proportional to the cross-sectional area of the conductor.
Mathematically, this is represented as:
The electrical resistance offered by a substance of unit length and unit cross-sectional area is called resistivity.
Ohmic and Non-Ohmic resistors
Resistors that follow Ohm’s Law are called Ohmic resistors and those which do not follow it are called Non-Ohmic resistors.
Superconductors
Conductors which offer zero resistance to the flow of current are called superconductors. Prominent examples of superconductors include aluminium, niobium, magnesium diboride, cuprates such as yttrium barium copper oxide and iron pnictides.
Combination of Resistors
Combination of resistors
- Two resistors are said to be combined in series if they carry the same current.
- Two resistors are said to be combined in parallel if the same potential difference is applied to them.
Equivalent Resistance of a system of resistors
The equivalent resistance of two resistors is given as:
- In series, Req=R1+R2
- In parallel, 1/Req= 1/R1+ 1/R2
EMF and Terminal Voltage
- EMF: The potential difference between the two terminals of a cell, when there is no current flowing through the circuit.
- Terminal voltage: The potential difference between the two terminals of a cell, when current is flowing through the circuit.
Electric Power and AC
Heating Effect of Current
Joule’s Law:
- 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 established, it causes electrons to move, i.e. flow of current.
Uses of Heating Effect of Electric Current
The heating effect of current is applied in the working of electrical heating appliances such as electric kettles, electric iron, room heaters, water heaters (geysers), etc.
To know more about the Heating Effect of Current, visit here.
Electric Power
- The rate of doing work or rate of consumption of electrical energy is called Electric Power. If W is work done in time t, then P=W/t.
- S.I unit is Watt(W). One watt of power is consumed when 1 A of current flows at a potential difference of 1 V.
- The commercial unit of electrical energy is a kilowatt-hour (kWh).
- 1kWh = 3,600,000J = 3.6×106J
- Represented as P=I2R and P=V2/R
- One kilowatt-hour is defined as the amount of energy consumed when 1kW of power is used for 1 hour.