"AKC SCIENCE CLASSES"
CLASS 10 TH (CBSE AND MP BOARD)
CHAPTER 12
ELECTRICITY
BASIC CONCEPTS
1) Frictional electricity :- The property due to which rubbed substances attract light objects is called electricity. The electricity developed by rubbing or friction is called frictional electricity.
2) Positive and negative charges :- The charge acquired by a glass rod when rubbed with silk is called positive charge and the charge acquired by an ebonite rod when rubbed with wool is called negative charge.
3) Fundamental law of electrostatics :- Like charges repel and unlike charges attract each other.
4) Coulomb's law :- The force of attraction or repulsion between two point charges is
- directly proportional to the product (qq) of the two charges and
- inversely proportional to the square of the distance (r) between them.
5) Coulomb :- It is the SI unit of charge. One coulomb is defined as that amount of charge which repels an equal and similar charge with a force of 9 ✖ 10⁹ N when placed in vacuum at a distance of 1 metre from it.
Charge on an electron = -1.6 ✖ 10⁻¹⁹ Coulomb.
6) Law of conservation of charge :- Electric charges can neither be created nor destroyed, they can only be transferred from one body to another.
7) Static and current electricities :- Static electricity deals with the electric charges at rest while the current electricity deals with the electric charges in motion.
8) Conductor :- A substance which allows passage of electric charges through it easily, is called a 'conductor'. A conductor offers very low resistance to the flow of current. For examples, copper, silver, aluminium, etc.
9) Insulator :- A substance that has infinitely high resistance does not allow electric current to flow through it. It is called an 'insulator'. For examples, rubber, glass, plastic, ebonite, etc.
10) Electric current :- The electric current is defined as the rate of flow of electric charge through any section of a conductor.
Electric current = Charge/Time or I = Q/t.
Electric current is a scalar quantity.
11) Ampere :- It is the SI unit of current. If one coulomb of charge flows through any section of a conductor in one second, then current through it is said to be one ampere.
12) Electric circuit :- The closed path along which an electric current flows is called an 'electric circuit'.
13) Conventional current :- Conventionally, the direction of motion of positive charges is taken as the direction of current is opposite to that of the negatively charged electrons.
14) Electric field :- It is the region around a charged body within which its influence can be experienced.
15) Electrostatic potential :- Electrostatic potential at any point in an electric field is defined as the amount of work done in bringing a unit positive charge from infinity to that point. Its unit is volt.
16) One volt potential :- The electrostatic potential at a point in an electric field is said to be one volt if one joule of work has to be done in bringing a positive charge of one coulomb from infinity to that point.
17) Potential difference between two points :- The potential difference between two points in an electric field is the amount of work done in bringing a unit positive charge from one point to another.
Potential difference = ----------------------
Or V = W/Q
18) One volt potential difference :- The potential difference between two points in an electric field is said to be one volt if one joule of work has to be done in bringing a positive charge of one coulomb from one point to another.
1 joule 1J
1 volt = ------------------ or 1V = -----------
1 coulomb 1C
19) Electrochemical or voltaic cell :- It is a device which converts chemical energy into electrical energy.
20) Galvanometer :- It is a device to detect current in an electrical circuit.
21) Ammeter :- It is a device to measure current in a circuit. It is a low resistance galvanometer and is always connected in parallel to the components across which the potential difference is to be measured.
22) Ohm's law :- This law states that the current passing through a conductor is directly proportional to the potential difference across its ends, provided the physical conditions like temperature, density, etc., remain unchanged.
V∝ I or V = RI
24) Resistance :- It is the property of a conductor by virtue of which it opposes the flow of current through it. It is equal to the ratio of the potential difference applied across its ends and the current flowing through it.
Resistance = --------------------------------- or R = ---------
Current I
25) Ohm :- It is the SI unit of resistance. A conductor has a resistance of one ohm if a current of one ampere flows through it on applying a potential difference of 1 volt across its ends.
1 Volt 1V
1 ohm = ------------------- Or 1 Ω = ----------
1 ampere 1A
26) Resistor :- A conductor which has some appreciable resistance is called a 'resistor'.
27) Factors on which resistance of a conductor depends :- The resistance R of a conductor depends on its length L, area of cross-section A and the nature of its material. It is given by
R = ρ --------
The proportionality constant ρ is called resistivity of the conductor.
28) Resistivity :- It is defined as the resistance offered by a cube of a material of side 1 m when current flows perpendicular to its opposite faces. Its SI unit is ohm-metre (Ω m).
29) Resistance in series :- When two or more resistances are joined end to end so that same current flows through each of them in turn, they are said to be connected in series. Here, the total resistance is equal to the sum of the individual resistances.
RS = R₁ + R₂ + R₃ + .........
30) Resistance in parallel :- When two or more resistances are connected across two points so that each of them provides a separate path for current, they are said to be connected in parallel. Here the reciprocal of their combined resistance is equal to the sum of the reciprocals of the individual resistances.
31) Heating effect of current :- When an electric current is passed through a conductor, heat is produced in it. This is known as heating effect of current.
32) Joule's law of heating :- It states that the heat produced in a conductor is directly proportional to
- the square of the current I through it
- proportional tp its resistance R and
- the time t for which current is passed.
33) Electric energy :- It is the total work done in maintaining an electric current in an electric circuit for a given time.
Electric energy, W = VIt = I²Rt joule
34) Electrical power :- Electrical power is the rate at which electric energy is consumed by an appliance.
P = W/t = VI = I²R = V²/R
35) Watt :- It is the SI unit of power. The power of an appliance is 1 watt if one ampere of current flows through it on applying a potential difference of 1 volt across its ends.
1 watt = ----------------- = 1 volt ✖ 1 ampere
36) Kilowatt hour :- It is the commercial unit of electrical energy. One kilowatt hour is the electric energy consumed by an appliance of 1000 watts when used for one hour.
1 Kilowatt hour (kWh) = 3.6 ✖ 10⁶ J
37) Power rating :- The power rating of an appliance is the electric energy consumed per second by the appliance when connected across the marked voltage of the mains.
38) Efficiency of an electric device :- It is the ratio of the output power to the input power.
Output power
