Current Electricity

When electrons move from a low to a high potential, they gain energy because they are moving against the electric field.

An ammeter is always connected in series to measure the current flowing through the circuit.

The resistance of a conductor does not depend on its density. It depends on length, cross-sectional area, and resistivity.

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points.

A short circuit is a condition where the resistance of a circuit becomes zero, allowing a large current to flow.

Ohm's law is valid only if the temperature remains constant, as resistance can vary with temperature.

Ohm's law is not applicable to semiconductors because their resistance varies non-linearly with voltage and current.

The net resistance \( R \) of two resistors \( R_1 \) and \( R_2 \) in parallel is given by \( \frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2} \). Thus, \( \frac{1}{R} = \frac{1}{6} + \frac{1}{12} = \frac{1}{4} \), so \( R = 4Ω \).

The property of a body to oppose the flow of electric charge through it is called electric resistance.

A battery is connected in an electric circuit to maintain a constant potential difference across the conductor, ensuring a steady flow of current.

A steady current refers to a continuous and constant flow of free electrons in a conductor.

Electric current is defined as the amount of charge \( Q \) passing through a point in a circuit per unit time \( t \), given by \( I = \frac{Q}{t} \).

Direct Current (DC) is an electric current that flows in one direction with a constant magnitude.

Alternating Current (AC) is an electric current that reverses its direction many times per second, typically used in household power supply.

Potential difference refers to the difference in electrical potential energy per unit charge between two points in an electric circuit.

Electromotive Force (EMF) is the energy per unit charge imparted by an energy source such as a battery or generator.

Ohm’s Law states that the voltage \( V \) across a conductor is directly proportional to the current \( I \) flowing through it, expressed as \( V = IR \).

Conductance is the measure of how easily electrical current can pass through a material, and it is the reciprocal of resistance.

In a series combination of resistors, the total resistance is the sum of the individual resistances.

In a parallel combination of resistors, the total resistance is given by the reciprocal of the sum of the reciprocals of the individual resistances.

Electric power represents the rate at which electrical energy is transferred or converted per unit time in a circuit.

Joule’s Law states that the heat produced in a conductor is proportional to the square of the current \( I \), the resistance \( R \), and the time \( t \), expressed as \( H = I^2 R t \).

A thermistor is a type of resistor whose resistance varies significantly with temperature, making it useful for temperature measurement and control.

A Light-Emitting Diode (LED) is a semiconductor device that emits light when an electric current flows through it.

An LDR (Light Dependent Resistor) changes its resistance based on the intensity of light it is exposed to, decreasing resistance with increasing light intensity.

A galvanometer is an instrument used to detect and measure small electric currents.

An ammeter is an instrument used to measure the electric current in a circuit, typically in amperes.

A voltmeter is an instrument used to measure the potential difference (voltage) between two points in an electric circuit.

Nikola Tesla used a Tesla coil to demonstrate wireless transmission of electrical energy, lighting up fluorescent lamps without wires.

In Tesla's wireless transmission experiments, the lamps were placed approximately 25 miles away from the power source.

The bulb lights up due to the magnetic field emitted by the Tesla coil, which wirelessly transmits electrical energy.

In electronic current, the flow of current is from the negative terminal to the positive terminal, which is the direction of electron flow.

Direct current (DC) is the type of current that flows only in one direction.

The frequency of alternating current (AC) in most power stations is 50 Hz, though it can be 60 Hz in some countries like the United States.

Potential difference refers to the difference in electrical potential energy per unit charge between two points in an electric field.

The unit of potential difference in the SI system is the volt (V).

One volt is defined as the potential difference that would move one coulomb of charge with one joule of energy.

Another common name for potential difference is voltage.

Electromotive force (EMF) is defined as the energy per unit charge supplied by a source to move charges from a lower potential energy to a higher potential energy.

The SI unit of electromotive force (EMF) is the volt (V).

The unit of electromotive force (EMF) in the centimeter-gram-second (CGS) system is the statvolt.

George Simon Ohm discovered the relationship between voltage and current, which is known as Ohm's Law.

According to Ohm’s Law, the current through a conductor is directly proportional to the potential difference (voltage) across it.

The correct formula representation of Ohm’s Law is \( V = IR \), where \( V \) is voltage, \( I \) is current, and \( R \) is resistance.

In the equation \( I = KV \), the constant 'K' represents conductance, which is the reciprocal of resistance.

The SI unit of resistance is the ohm (Ω).

Ohm’s Law is only valid under the condition that the temperature remains constant, as resistance can vary with temperature changes.

A diode is a non-ohmic device because it does not follow Ohm's Law. Its resistance changes with the direction and magnitude of the current.

Ohm’s Law does not apply directly to capacitive and inductive circuits because these components introduce reactance, which affects the relationship between voltage and current.

Using Ohm's Law \( V = IR \), the voltage drop is \( V = (300 \times 10^{-6} \, \text{A}) \times (50 \times 10^3 \, \Omega) = 15 \, \text{V} \).

The formula given by Ohm’s law is \( V = IR \), where \( V \) is voltage, \( I \) is current, and \( R \) is resistance.

The unit of electrical resistance is the ohm (Ω).

Electrical resistance measures the opposition to the flow of electric charge in a circuit.

Resistance is directly proportional to the length of the conductor. As the length increases, the resistance also increases.

The formula for resistance \( R \) in terms of resistivity \( \rho \), length \( L \), and cross-sectional area \( A \) is \( R = \frac{\rho L}{A} \).

The unit of resistivity is the ohm-meter (Ω·m).

Insulators have higher resistivity compared to conductors and semiconductors, as they strongly oppose the flow of electric charge.

In metallic conductors, resistance increases with an increase in temperature due to increased atomic vibrations that impede electron flow.

A series combination of resistors is also known as a voltage divider because the voltage across each resistor is a fraction of the total voltage supplied.

In a series circuit, there is only one path for current to flow through all the components.

In a series circuit, the total or equivalent resistance \( R_e \) is the sum of all individual resistances.

In a series circuit, if one component stops working, the entire circuit stops working because the current has only one path and it is interrupted.

In a series connection, the total voltage is the sum of the individual voltages across each component.

The equivalent resistance \( R_e \) in a parallel circuit is given by the reciprocal of the sum of the reciprocals of the individual resistances: \( \frac{1}{R_e} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \).

In a parallel circuit, the voltage remains the same across all resistors because each resistor is connected directly across the voltage source.

The total resistance in a series circuit is the sum of the individual resistances: \( 100Ω + 400Ω + 200Ω = 700Ω \).

The formula to calculate energy in kilowatt-hours (kWh) is \( \text{Energy (kWh)} = \frac{\text{Power (W)} \times \text{Time (hr)}}{1000} \).

Electric power refers to the rate at which electrical energy is transferred or converted per unit time in a circuit.

The correct mathematical expression for electric power \( P \) is \( P = IV = I^2R = \frac{V^2}{R} \).

Electrical energy is measured in joules (J).

According to Joule's Law, the heat produced \( H \) in a conductor is directly proportional to the square of the current \( I \), the resistance \( R \), and the time \( t \), expressed as \( H = I^2 R t \).

The significance of Joule’s Law in electrical circuits is that it quantifies the amount of heat generated when an electric current flows through a conductor.

Using Joule's Law \( H = I^2 R t \), we find \( 100J = I^2 \times 4Ω \times 1s \). Solving for \( I \) gives \( I = 5A \). Then, using \( V = IR \), the potential difference \( V = 5A \times 4Ω = 20V \).

The primary function of a resistor is to provide a specified resistance in a circuit, which can be used to control the flow of electrical current.

A battery converts chemical energy into electrical energy through electrochemical reactions.

A microphone is a component that converts sound energy into electrical signals.

The resistance of an LDR (Light Dependent Resistor) decreases when the light intensity increases.

LDRs are mostly used in automatic security lights, where they help in detecting light levels to switch the lights on or off.

A thermistor is a device that is sensitive to temperature changes, altering its resistance as the temperature changes.

A galvanometer is an instrument used to detect and measure very small electric currents.

An ammeter is a modified form of a galvanometer, designed to measure larger currents.

In an ammeter, a shunt resistance is connected in parallel to allow most of the current to bypass the galvanometer, enabling measurement of larger currents.

A voltmeter is an instrument used to measure the potential difference (voltage) between two points in an electric circuit.

To convert a galvanometer into a voltmeter, a high resistance is connected in series to limit the current flow and measure potential difference.

The earth wire carries no current under normal conditions but is used for safety to prevent electric shock by grounding any leakage current.

Electrical appliances in homes are connected in parallel so that each appliance can operate independently at the same voltage.

A fuse is a safety device that cuts off the current in a circuit if it exceeds a safe value, preventing damage or fire hazards.

Circuit breakers are used in place of fuses to provide overcurrent protection that can be reset, unlike fuses which need replacement after they blow.

A bimetallic strip in a circuit breaker reacts to heat generated by excessive current, causing it to bend and trip the circuit breaker.