Electricity Notes Class 10
Electricity Notes Class 10: CBSE Notes Class 10 Science Chapter 12 Notes. Electricity Notes PDF. Class 10 Science Chapter 12 Revision Notes – Electricity.
Electricity Notes Class 10: Overview
Electricity Notes Class 10 |
|
Board |
CBSE / NCERT |
Class |
10 |
Subject |
Science |
Chapter Number |
12 |
Chapter Name |
Electricity |
Topic |
Notes |
Electricity Notes Class 10 Science
An electric energy is the most reliable source of energy available in the modern era. Due to its convenient mode of operating, it has varieties of uses in industrial section, household purpose, and educational institutes.
Electric current:
Every metal consist of some loosely bounded electrons in its last orbit. These electrons can made available for conduction if any external source of energy is given, and acts as charge carriers. When these charges are flows through the metal wire constitutes an electric current.
Electric current is defined as the amount of flow of charges through given cross-section of conductor in given unit time OR the rate of flow of charge.
If q is net charge flows through conductor in unit time t then,
∴ I = q/t
SI unit of charge is coulomb and that of time is second, hence the SI unit of electric curretn is coulomb/second. Sir A.Ampere has invented the instrument for measurement of current, in his honour we use ‘ampere’ as unit of current
If 1 coulomb of charge flows through the conductor for 1 second , then current is said to be equal to 1 ampere
∴ 1 A = (1 C)/(1 s)
Current is generally expressed in small units like mA, µA etc
Where 1 mA= 10-3 A, 1 µA=10-6A
Ammeter is always connected in series with the circuit.
The direction of flow of electron is from negative terminal of cell to positive terminals, but the conventional current is always considered from positive terminal to negative terminal of cell.
Drift Speed:
Motion of flow of electron in conductor is very different than that of motion in empty space. In presence of applied electric field path of all electrons is disturbed by certain force and they gets pushed towards the positive end of electric energy with certain average speed, this speed is known as ‘drift speed’.
Potential difference:
Electrons in metal wire flows only when there is the difference of energy at both the terminals of wire. This difference is maintained by the device like cell. The chemical reaction within electrodes of cell maintains the difference at the ends of wire, this difference is known as ‘potential difference’.
During motion of electron, they gets drifted in direction of electric field under action of force due to electric field, this force is merely called as electromotive force whose function is to pull electrons from one end to other. This makes electrons (charges) to do work in electric field.
The amount of work done by unit positive charge in moving from one end to other is called as potential difference.It is denoted as ‘V’
Potential difference between two terminals of conductor is the as,
∴ V = W/Q
SI unit of work is joule and charge is coulomb, hence the SI unit of potential difference is joule/coulomb OR J/C. As the first cell (battery) were discovered by Sir Alessandro Volta, SI unit of potential difference is named after him as ‘volt’ (V).
If 1 joule of work is done in displacing of 1 coulomb of charge, then the potnetial difference is said to be equal to 1 volt.
∴1 V=(1 J)/(1 C)
Electric circuit:
Electric circuit is defined as the arrangement of electric components in such a manner that it forms a closed network through which continuous flow of current is takes place. The representation electric circuit using symbols for given component is called as electric circuit diagram.
Some electric components with their symbols:
Ohm’s law:
Experimentally it is proven that, if physical condition of conductor remains the same, electric current increases linearly with increase in potential difference. This was proven practically by Sir George Ohm, and gives rise to law known as Ohm’s law.
Ohm’s law stated that, the electric current flowing through the metallic conductor is directly proportional to the potential difference applied across terminals of conductor provided the physical conditions of conductor remains same.
When physical conditions such as length of conductor, area of cross-section, temperature and material of conductor kept constant then,
The proportionality constant represented as ‘R’ is known as the resistance of material of wire. The graph of potential difference verses electric current is always a straight line and passes through origin, as shown above.
Resistance is the property of material by virtue of which it opposes the flow of electrons in it. On the basis of resistance materials are divided as
- Insulators: Substance which posses high resistance to flow of electron e.g. rubber, wood etc
- Conductors: Substance which posses low resistance to flow of electron e.g. copper, aluminium etc
- Semiconductors: Substance which posses moderate resistance to flow of electron. E.g. Silicon, Germanium etc.
Resistivity:
Keeping material and temperature of conductor same if we change the length and area of cross section of conductor, it is observed that the resistance is depends upon a length and area of cross-section of conductor.
Suppose we connect a wire of length ‘L’ and area of cross section ‘A’ across potential difference ‘V’ then current in circuit is ‘I’. Case: 1) if we replace the wire of double the length with same potential difference and area of cross section, current appears to be half of the previous value, indicates that the resistance of conductor is directly proportional to length ‘L’ of conductor.
Case: 2) Keeping same length and material doubling the area of cross section, we will get current increase twice than previous value, which indicates the resistance of conductor is inversely proportional to area of cross section. Then from case 1) and case 2) we can say,
Here ρ is constant of proportionality called as resistivity or specific resistance of material From above equation we can find value of specific resistance as
SI unit of resistivity is ohm-meter (Ω.m)
The reciprocal of resistivity is known as conductivity denoted as ‘σ’
∴ σ = 1/ρ
SI unit of conductivity is siemen (S)
Combination of resistance:
Resistor is a device used to offer resistance in electric circuit. To control amount of current flow in circuit the resistors are connected either in series or in parallel as per the requirement of the device.
- Resistors in series: To increase effective resistance of circuit so as to limiting value of current flow, resistors are connected in series.
If three resistors of resistances R1, R2, and R3 are connected in series, shown in figure below
- The current remains the same throughout the circuit.
- Potential difference across each resistor is different.
- Total potential difference is equal to sum of potential drops across each resistor.
- Equivalent resistance (RS) of circuit is greater than that of individual resistance and is equal to sum of individual resistance.
For ‘n’ number of resistors Rs= R1+R2+R3+……………+Rn
- Resistors in parallel: To decrease effective resistance of circuit so as to increase the value of current flow, resistors are connected in parallel.
If three resistors of resistances R1, R2, and R3 are connected in parallel as shown in fig below
- The potential difference remains the same throughout the circuit.
- Current across each resistor is different.
- Total current is equal to sum of current across each resistor.
4.Equivalent resistance (RP) of circuit is less than that of individual resistance and is equal to sum of reciprocal individual resistance.
For ‘n’ number of resistors 1/RP= 1/R1+1/R2+1/R3+……………+1/Rn
Heating effect of electric current:
Continuous flow of current in conductor increases the temperature of conductor which gives rise to heat. Large number of electron flows from one end to another end in conductor in electric field. The electron consistently collide on ions boundaries and on neighbouring atoms so electrons has to do work against the frictional forces which results in dissipating in its kinetic energy. As per the law of conservation of energy this dissipated kinetic energy could be regain by producing heat energy due to frictional force caused by collisions of electron and temperature of conductor starts rising. This phenomenon is known as heating effect of electric current.
Increase in temperature of conductor when current passing through it is known as heating effect of electric current.
If conductor of resistance ‘R’ carries current ‘I’ when connected, across cell of p.d. ‘V’ for time‘t’ then,
H = I2.R.t This equation is also known as Joule’s law of heating effect.
Applications of heating effect of electric current:
- Electric bulb: The filament used in bulb is made of tungsten whose melting point is around 34000C. When current passes through this filament, its temperature start rises and colour also changes to yellowish orange. This yellow colour emitted by filament of tungsten used as sources of light during darkness of night. The glass coating is provided with noble gas so that the heat produced in the bulb can get absorbed.
- Electric fuse: It is used as a safety device for domestic appliances. It is connected in series with the live wire. It consist of wire made up of an alloy of lead and tin has low melting point about 2000C, when excess current passes through this fuse wire it gets heated immediately and melts due to overheating and disconnects the main circuit automatically so that we can prevent our appliances from getting damaged.
Electric power:
Electric power is defined as the rate of dissipation of electric energy or rate of doing work by the charges in an electric field.
If conductor of resistance ‘R’ carries current ‘I’ when connected, across cell of p.d. ‘V’ for time‘t’ then,
Electric power, P= W/t or P=W.t
∴ P = V.I or P = I2 R (by Ohm’s law, V = I.R
SI unit of power is named after Sir James Watt as watt (W)
Electric power generally measured in larger scale, hence the preferred units of power are
- 1 kilowatt= 1000 watt
- 1 horsepower (1 hp) = 746 watt
Note that when we use any electric instrument of power rating 1000 watt for 1 hour then the consumption of electric energy is read as 1 unit.
1 unit of electric energy = 1000 watt × 1 hour
= 1 kW. h
= 1000 ×3600 watt. second
= 3.6 ×106 J
i.e. when we spend 3.6 ×106 J of electric energy, electricity board charges us for 1 unit.