16. Current Electricity

 Current Electricity:

Electric current is how fast electric charge is moving through something. Imagine it like water flowing through a pipe. The unit for current is the ampere(A), and it's a scalar, meaning it has no direction. If one ampere of current flows through a wire, it means a lot of tiny particles called electrons are moving through it. Specifically, 6.25 × 10¹⁸ electrons pass through in one second.

Resistance:

Resistance is like a roadblock for electric current flowing through a material. It happens because the moving electrons bump into the atoms in the material. We measure resistance in ohms.

Ohms law:

Ohm's Law tells us that if nothing changes, like temperature or light, the current flowing through something is directly related to the voltage across it. If we have a voltage (V) and a current (I), we can use the formula V = IR, where R is the resistance.

Ohmic Resistance:

Ohmic resistance is when a material follows Ohm's law, meaning the resistance stays constant as the current changes. For instance, the resistance of a manganin wire behaves this way.

Non ohmic resistance:

Non-ohmic resistance is when a material doesn't follow Ohm's law, so the resistance changes as the current changes. Examples include the resistance of diode and triode valves.

Conductance :

Conductance (G) is the opposite of resistance (R), meaning it's how easily electricity flows through a material. It's represented by the formula G=R1​. The unit for conductance is ohm⁻¹, also known as mho or siemen.

The resistance of a material depends on its length (l) and inversely on its cross-sectional area (A). If we denote the resistance as R, the formula is R=ρ×Al , where ρ is a constant called resistivity, specific to the material. Resistivity is measured in ohm meters.

Specific conductance or conductivity:

Specific conductance or conductivity (σ) is the opposite of resistivity (ρ). It tells us how easily a material conducts electricity. The formula for conductivity is σ = 1/ρ. The unit for conductivity is mho per meter (mho/m) or siemen per meter (S/m).

Combination of Resistance :

When resistors are combined in circuits, there are two main ways: series and parallel.

In series, you just add up all the resistances to find the total resistance: $𝑅={𝑅}_1+{𝑅}_2+\dots +{𝑅}_{𝑛}$.

In parallel, it's a bit different. You add up the reciprocals of each resistance to find the reciprocal of the total resistance: $\frac{1}{𝑅}=\frac{1}{{𝑅}_1}+\frac{1}{{𝑅}_2}+\dots +\frac{1}{{𝑅}_{𝑛}}$.

Electric Power :

Electric power is how quickly electrical energy is used up in a circuit, measured in watts.

Kilowatthour :

A kilowatt-hour (kWh) is a unit of energy, representing the amount of energy used when a circuit consumes 1 kilowatt (1000 J/s) for 1 hour. It's equal to 3.6 x 10^6 joules. Also known as a board of trade unit.

Ammeter:

An ammeter measures electric current in a circuit and is connected in series. It has zero resistance.

Voltmeter:

A voltmeter measures the potential difference between two points in a circuit and is connected in parallel. It has infinite resistance.

Electric fuse :

An electric fuse is a safety device placed in series with an electrical appliance to protect it from damage caused by excessive current. Typically, it's a small wire made of an alloy of copper, tin, and lead with a low melting point.

A pure fuse is made entirely of tin.

Galvanometer :

A galvanometer is a device used to detect and measure small electric currents, typically up to 10 amperes. It's like a sensitive meter for electricity.

Shunt :

A shunt is a wire with very low resistance that's used with a galvanometer to measure larger currents. When connected in parallel with the galvanometer, it allows the measurement of higher currents.

To turn a galvanometer into an ammeter, you connect shunts in parallel with it. And to turn it into a voltmeter, you connect a very high resistance in series with it.

Transformer :

A transformer is a device that changes the voltage of alternating current (AC). It can increase voltage from low to high or decrease it from high to low, based on electromagnetic induction. Transformers work only with AC.

A.C. Dynamo (or generator) :

An AC dynamo, also known as a generator, is a machine that turns mechanical energy into electrical energy. It operates based on the principle of electromagnetic induction.

Electric motor :

It is a device which converts mechanical energy into electrical energy.

Microphone :

A microphone converts sound energy into electrical energy using electromagnetic induction. It's a tool that changes sound waves into electrical signals, which can then be amplified, transmitted, or recorded.

Power stations generate alternating current (AC) electricity, typically at voltages of 22,000 volts or higher. To reduce energy loss during long-distance transmission, transformers at grid substations increase the voltage to around 132,000 volts.