Basic Electricity STD 9
विजेच्या मूलभूत गोष्टींबद्दल मार्गदर्शन
The four most basic physical quantities in electricity are:
Voltage (V)
Current (I)
Resistance (R)
Power (P)
Each of these quantities is measured using different units:
Voltage is measured in volts (V)
Current is measured in amps (A)
Resistance is measured in ohms (Ω)
Power is measured in watts (W)
Electrical power, or the wattage of an electrical system, is always equal to the voltage multiplied by the current.
A system of water pipes is often used as an analogy to help people understand how these units of electricity work together. In this analogy, voltage is equivalent to water pressure, current is equivalent to flow rate and resistance is equivalent to pipe size.
In electrical engineering, there is a basic equation that explains how voltage, current and resistance relate. This equation, written below, is known as Ohm's law.
Ohm's Law-If the physical state of a conductor remains constant, the current (I) flowing through it is directly proportional to the potential difference (V) between its two ends.
V = I x R
Ohm's law states that voltage is equal to the current flowing in a circuit times the resistance of the circuit.
I = kV ( k = constant of proportionality)
= V ( = R = Resistance of the conductor )
= V Hence V = IR
This is known as Ohm’s law.
We can obtain the SI unit of resistance from the above formula, Potential difference and current are measured in Volts and Amperes respectively. The unit of resistance is called Ohm. It is indicated by the symbol W.
= 1 Ohm (W)
VOLTAGE-
Volts are the base unit used to measure Voltage. One volt is defined as the "difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points." The volt is named after the Italian physicist Alessandro Volta.
Object Voltage
Single-cell, rechargeable battery
1.2V
Single-cell, non-rechargeable battery (Pencil cell AAA)
1.5V–1.56V
USB
5V
Automobile battery
2..1V per cell / 12 V battery
Electric vehicle battery
400V
Household outlet (Europe, Asia, Africa, Australia)
230V
High-voltage electric power lines (Tower line)
110,000V
Lightning
100,000,000V
O
Ampere
The ampere, often shortened to "amp" or A, is the base unit of electric current in the International System of Units. It is named after the French mathematician and physicist André-Marie Ampère, who is considered the father of electrodynamics.
Electricity consists of the flow of electrons through a conductor, for example, an electric wire or cable. We measure the rate of flow of electricity as an electric current (just as we think of the rate of flow of water in a river as the river current). The letter used to represent current in an equation is I.
Electric current is measured in Amperes, shortened to Amps or simply the letter A.
Resistance
Ohms are the base unit of resistance in an electrical system. The ohm is defined as "an electrical resistance between two points of a conductor when a constant potential difference of one volt, applied to these points, produces in the conductor a current of one ampere, the conductor not being the seat of any electromotive force." The ohm is named after the German physicist Georg Simon Ohm.
Resistance is measured in ohms, or Ω (omega), for short. So, Ten ohms can be written 10Ω
Resistivity ρ : At a given temperature, the resistance (R) of a conductor depends on its length (L), area of cross-section (A) and the material it is made of.
It is denoted by ρ(RHO)and its unit is Ωm (ohm metre)
If the resistance of a conductor is R, then
Also then
Then where ρ is constant of proportionality
It is resistivity of particular material.
Current electricity is the movement of electrons from a source of electrons such as a battery or solar cell along a path such as a copper wire. The electric current carries energy from the source to an electrical device called a load (light bulb, motor) that converts the electrical energy to a useful form.
a light bulb converts electrical energy to light energy
a motor converts electrical energy to kinetic energy.
Once the current passes through the load(resistance), it returns to the source where the cycle begins again.
An electric current is a flow of electric charge in a circuit. More specifically, the electric current is the rate of charge flow past a given point in an electric circuit.
The magnitude of the electric current is measured in coulombs per second, the common unit for this being the Ampere or amp which is designated by the letter ‘A’.
Conventional current flow: The conventional current flow is from positive to the negative terminal and indicates the direction that positive charges would flow.
Electron flow: The electron flow is from negative to positive terminal. Electrons are negatively charged and are therefore attracted to the positive terminal as unlike charges attract.
Electric power definition:
Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. It is the rate of doing work.
In terms of an electric circuit, electrical power is the rate, per unit time, at which electrical energy is transferred by an electric circuit.
From the definition it can be seen that:
W =V Q/t
But as:
=Current, I
Substituting:
W=V I
Where: W = power in watts
V = potential in volts
I = current in amps
Q = charge in coulombs
t = time in seconds
W= i.e. W = I2R
.
Series and parallel circuit
Series circuit ..
.Rs =R1 +R2 +R3
parallel circuit
Rp – effective R is reciprocal of 1/(Rp ) = 1/R1+1/R2+1/R3