Ohms And Resistance

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Electric current Ohm’s law and Resistance

 

Electrical current is the flow of charged particles. The flow of charges will be constant in current electricity. Electric current flows from higher electric potential to lower electric potential. For the current to flow, it requires a circuit which is closed loop of a conducting material. The circuit consists of wires which are connected end to end and the electrons flow in same direction.

A circuit has Conductors (wire), switch, load and a power source. The circuit starts and stops at the same point. Usually copper wires are used as conductors without insulation. It is through the conductor the current flows. A switch is used to open or close the circuit. When the switch is closed current flows through the circuit and when the switch is open, it breaks the circuit and no current flows through it. A cell can be the power source. If we put more than one cell it becomes a battery.

The load which is also known as Resistor uses the electrical energy and converts it into some other form of energy. It can be a Light bulb or anything else. If there is no load in the circuit then it will be a short circuit.

 

Electric Current is measured in amperes (amps) by an ammeter which will be connected in series with other components in a circuit. Current, I = Q / t, where Q is the charge in coulombs and t is the time in seconds. 

Voltage is defined as the electrical potential difference between two points in a circuit. The unit of voltage is volts. The unit is derived from the name Alessandro Volta. Cells or batteries provide the voltage or the potential difference which is required.

Resistance resists the flow of current. It is the measure of an objects ability to hold off the flow of electrons. The resistance will be low in a conductor and high in an insulator. It is measured in ohms. The unit ohm is named after the scientist Georg Simon ohm who formulated the ohm’s law.

Resistors are used to control the flow of electric current in a circuit. It converts electrical energy into heat and light. A resistor is a passive component as they consume power but will not generate power. They are usually made up of Metal, carbon or with metal oxide film. Resistors are used for limiting the current and to protect the semiconductor devices like LED. It is also used to limit the frequency response in a filter circuit.

 


Ohm’s Law


 

Georg Simon Ohm showed the relationship between voltage, current and resistance and formulated the ohm’s law. This law is the basis of electricity.

The law states that V = I R, where voltage V is in volts, Current I in amps and resistance R in ohms.

Thus I = V / R and R = V / I.


 


 


Series and Parallel Connections


 

There are mainly two types of circuits, Series and Parallel. Both series and parallel circuits consists of more than one load. Resistors can be connected both in series, parallel or a combination of both.

In series circuit electrons travel only in one path. Here the current will be the same which passes through each resistor. The voltage across resistor in a series connection will be different. In series connection if one resistor is broken or any fault occurs, the entire circuit is turned off. Series circuits do not overheat easily. The design of series circuit is simple compared to parallel circuits.

  • In brief, When two or more resistances are connected end to end then they are said to be connected in series combination.

Some Christmas tree lights can be in series circuits. If one bulb goes off the entire string goes out. 

In parallel circuit electrons travel through many branches in it. In this case the voltage remains the same across each resistors in the circuit. Here the current in the circuit is divided among each branches and finally recombines when the branches meet at a common point. A parallel circuit can be formed in many ways, which means resistors can be arranged in different forms. It can be used as a current divider.

  • In brief, When two or more resistances are connected between the same two points they are said to be connected in parallel combination.

 

In most cases the circuits are connected in parallel. This is because if one resistor is broken or damaged, it won’t turn off the entire system. But due to this effect, it is difficult to detect the failure if anything goes wrong in the circuit and thus it can be dangerous at certain times. It is easy to connect or disconnect a new resistor or other component without affecting the other Elements in the parallel circuit. But it uses a lot of wires and hence becomes complex. Mostly in buildings and houses we use parallel connection.

 

A third type of circuit involves the dual use of series and parallel connections in a circuit; such circuits are referred to as compound circuits or combination circuits. The circuit depicted at the right is an example of the use of both series and parallel connections within the same circuit. In this case, light bulbs A and B are connected by parallel connections and light bulbs C and D are connected by series connections. This is an example of a combination circuit.

 


Ohms Law Example

For the circuit shown below find the Voltage (V), the Current (I), the Resistance (R) and the Power (P).

 

Voltage   [ V = I x R ] = 2 x 12Ω = 24V

Current   [ I = V ÷ R ] = 24 ÷ 12Ω = 2A

Resistance   [ R = V ÷ I ] = 24 ÷ 2 = 12 Ω

Power   [ P = V x I ] = 24 x 2 = 48W

 


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Ohm’s Law

Ohm’s law is a law in electricity that states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance of the conductor.

The law is named after Georg Ohm, who discovered it in 1826. Ohm’s law is one of the most important laws in electricity, and it is used to calculate the current, voltage, and resistance in electrical circuits.

Resistance

Resistance is the opposition to the flow of electric current. It is measured in ohms (©). The higher the resistance, the lower the current flow.

Resistance is caused by the collisions of electrons with the atoms in the conductor. The more collisions, the higher the resistance.

The resistance of a conductor can be calculated using the following formula:

R = ÁL/A

where:

R = resistance (©)

Á = resistivity (©-m)

L = length of conductor (m)

A = cross-sectional area of conductor (m2)

Resistivity

Resistivity is a measure of how difficult it is for an electric current to flow through a material. It is measured in ohm-meters (©-m).

The resistivity of a material depends on its temperature and composition. The resistivity of most materials increases with temperature.

The resistivity of a material can be calculated using the following formula:

Á = Á0(1 + ±T)

where:

Á = resistivity at temperature T (©-m)

Á0 = resistivity at temperature T = 0 (©-m)

± = temperature coefficient of resistivity (1/°C)

Conductors and Insulators

Conductors are materials that allow electricity to flow through them easily. Insulators are materials that do not allow electricity to flow through them easily.

The difference between conductors and insulators is due to the way their atoms are arranged. In conductors, the atoms are loosely packed, which allows the electrons to move freely. In insulators, the atoms are tightly packed, which prevents the electrons from moving freely.

Some common conductors are metals, such as copper, silver, and gold. Some common insulators are plastics, rubber, and glass.

Series and Parallel Circuits

A series circuit is a circuit in which the components are connected in a single path. The current flows through all of the components in the same order.

A parallel circuit is a circuit in which the components are connected in multiple paths. The current can flow through any of the paths.

In a series circuit, the total resistance is equal to the sum of the individual resistances. In a parallel circuit, the total resistance is equal to the reciprocal of the sum of the reciprocals of the individual resistances.

Voltage Drop

Voltage drop is the decrease in voltage that occurs when current flows through a resistance. The voltage drop is equal to the product of the current and the resistance.

The voltage drop can be calculated using the following formula:

”V = IR

where:

”V = voltage drop (V)

I = current (A)

R = resistance (©)

Current Flow

Current flow is the movement of electric charge through a conductor. The current is measured in amperes (A).

The current flow is equal to the voltage divided by the resistance.

I = V/R

where:

I = current (A)

V = voltage (V)

R = resistance (©)

Power

Power is the rate at which work is done. It is measured in watts (W).

The power is equal to the voltage times the current.

P = VI

where:

P = power (W)

V = voltage (V)

I = current (A)

Electrical Safety

Electricity can be dangerous if it is not used safely. There are a few things you can do to stay safe around electricity:

By following these safety tips, you can help to prevent electrical accidents.

Here are some frequently asked questions and short answers about electricity:

Sure. Here are some MCQs without mentioning the topic Ohms and Resistance:

  1. What is the unit of electrical resistance?
    (A) Ohm (©)
    (B) Volt (V)
    (C) Ampere (A)
    (D) Coulomb (C)

  2. What is the formula for electrical resistance?
    (A) R = V/I
    (B) R = I/V
    (C) R = P/I
    (D) R = I^2/P

  3. What is the difference between voltage and current?
    (A) Voltage is the force that pushes current through a circuit, while current is the flow of electrons.
    (B) Voltage is the flow of electrons, while current is the force that pushes electrons through a circuit.
    (C) Voltage and current are the same thing.
    (D) Voltage and current are inversely proportional.

  4. What is the difference between direct current (DC) and alternating current (AC)?
    (A) DC is the flow of electrons in one direction, while AC is the flow of electrons in two directions.
    (B) DC is the flow of electrons in two directions, while AC is the flow of electrons in one direction.
    (C) DC and AC are the same thing.
    (D) DC and AC are inversely proportional.

  5. What is a resistor?
    (A) A resistor is a device that converts electrical energy into heat energy.
    (B) A resistor is a device that converts heat energy into electrical energy.
    (C) A resistor is a device that stores electrical energy.
    (D) A resistor is a device that conducts electrical energy.

  6. What is a capacitor?
    (A) A capacitor is a device that stores electrical energy.
    (B) A capacitor is a device that converts electrical energy into heat energy.
    (C) A capacitor is a device that converts heat energy into electrical energy.
    (D) A capacitor is a device that conducts electrical energy.

  7. What is an inductor?
    (A) An inductor is a device that stores electrical energy.
    (B) An inductor is a device that converts electrical energy into heat energy.
    (C) An inductor is a device that converts heat energy into electrical energy.
    (D) An inductor is a device that conducts electrical energy.

  8. What is a transformer?
    (A) A transformer is a device that converts electrical energy from one voltage to another.
    (B) A transformer is a device that converts electrical energy from one current to another.
    (C) A transformer is a device that converts electrical energy from one frequency to another.
    (D) A transformer is a device that converts electrical energy from one type to another.

  9. What is a rectifier?
    (A) A rectifier is a device that converts alternating current (AC) to direct current (DC).
    (B) A rectifier is a device that converts direct current (DC) to alternating current (AC).
    (C) A rectifier is a device that converts electrical energy into heat energy.
    (D) A rectifier is a device that converts heat energy into electrical energy.

  10. What is an inverter?
    (A) An inverter is a device that converts direct current (DC) to alternating current (AC).
    (B) An inverter is a device that converts alternating current (AC) to direct current (DC).
    (C) An inverter is a device that converts electrical energy into heat energy.
    (D) An inverter is a device that converts heat energy into electrical energy.

I hope these MCQs are helpful!

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