Ch-12 ELECTRICITY MIND MAP... [made by Kate Franson 10-d]

1. Electric current is expressed by the amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges.

1.1. The electric current is expressed by a unit called ampere (A), named after the French scientist, Andre-Marie Ampere (1775–1836).

1.2. One ampere is constituted by the flow of one coulomb of charge per second, that is, 1 A = 1 C/1 s

1.3. Small quantities of current is measured in milliampere (1 mA = 10–3 A) or in microampere (1 μA = 10–6 A).

1.4. An instrument called ammeter measures electric current in a circuit. It is always connected in series in a circuit through which the current is to be measured.

2. HEATING EFFECT OF ELECTRIC CURRENT

2.1. The heating effects of electric current depend on three factors:

2.1.1. The resistance of the conductor. A higher resistance produces more heat.

2.1.2. The time for which the current flows. The longer the time the amount of heat production is high.

2.1.3. Higher the current the amount of heat generation is also large.

2.2. Hence the heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by H = I^2 Rt. This equation is the Joule’s equation of electrical heating.

2.2.1. Joule’s law states the amount of heat production in a conductor is :

2.2.1.1. Directly proportional to the square of electric current flowing through it.

2.2.2. Is directly proportional to the resistance of the conductor.

2.2.2.1. Directly proportional to the time for which electric current flows through the conductor.

3. Made by- Kate Franson Davis (10-D) science

4. Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges.

4.1. If a net charge Q, flows across any cross-section of a conductor in time t, then the current I, through the cross-section is I=Q/t

4.2. The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 × 1018 electrons

4.3. (We know that an electron possesses a negative charge of 1.6 × 10–19 C.)

5. ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE

5.1. For flow of charges in a conducting metallic wire, the gravity, of course, has no role to play; the electrons move only if there is a difference of electric pressure – called the potential difference – along the conductor.

5.2. This difference of potential may be produced by a battery, consisting of one or more electric cells. The chemical action within a cell generates the potential difference across the terminals of the cell, even when no current is drawn from it.

5.3. Potential difference (V) between two points = Work done (W )/Charge (Q) V=W/Q

5.4. The SI unit of electric potential difference is volt (V), named after Alessandro Volta (1745–1827), an Italian physicist.

5.5. One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other.

5.6. 1 volt = 1 joule/1 coulomb

5.7. The potential difference is measured by means of an instrument called the voltmeter. The voltmeter is always connected in parallel across the points between which the potential difference is to be measured.

6. ELECTRIC POWER

6.1. The rate at which electric energy is dissipated or consumed in an electric circuit is known as electric power

6.2. The power P is given by P = VI Or P = I^2R = V^2/R

6.3. The SI unit of electric power is watt (W). It is the power consumed by a device that carries 1 A of current when operated at a potential difference of 1 V. Thus,

6.4. 1W = 1volt×1ampere= 1 VA

6.5. The unit ‘watt’ is very small. Therefore, in actual practice we use a much larger unit called ‘kilowatt’. It is equal to 1000 watts.

6.6. Since electrical energy is the product of power and time, the unit of electric energy is, therefore, watt hour (W h).

6.6.1. 1 kW h = 1000 watt × 3600 second 3.6 × 10^6 watt second 3.6 × 106 joule (J)

6.6.2. One watt hour is the energy consumed when 1 watt of power is used for 1 hour. The commercial unit of electric energy is kilowatt hour (kW h), commonly known as ‘unit

7. OHM’S LAW

7.1. In 1827, a German physicist Georg Simon Ohm (1787–1854) found out the relationship between the current I, flowing in a metallic wire and the potential difference across its terminals

7.2. He stated that the electric current flowing through a metallic wire is directly proportional to the potential difference V, across its ends provided its temperature remains the same. This is called Ohm’s law. In other words

7.3. V ∝ I or V/I = or V=constant =R V= IR

7.4. In the equation above R is a constant for the given metallic wire at a given temperature and is called its resistance. It is the property of a conductor to resist the flow of charges through it. Its SI unit is ohm, represented by the Greek letter Ω. According to Ohm’s law, R = V/I

7.5. If the potential difference across the two ends of a conductor is 1 V and the current through it is 1 A, then the resistance R, of the conductor 1 volt is 1Ω.That is, 1ohm=1 volt/ 1 ampere

7.6. from the equation above we get I = V/R

8. FACTORS ON WHICH THE RESISTANCE OF A CONDUCTOR DEPENDS

8.1. Resistance is defined as the opposition to the flow of electrical current through a conductor. The resistance of an electric circuit can be measured numerically

8.2. Conductivity and resistivity are inversely proportional. The more the conductive, the less resistance it will have.

8.3. Resistance = Potential difference/ Current

8.4. The resistance of the conductor depends on the following factors:

8.4.1. 1. The temperature of the conductor 2. The cross-sectional area of the 3.conductor 4. Length of the conductor 5.Nature of the material of the conductor

8.5. Precise measurements have shown that resistance of a uniform metallic conductor is directly proportional to its length (l) and inversely proportional to the area of cross-section (A). That is, R ∝ L and R ∝ 1/A or l R∝A , R = ρ Al

8.6. where ρ (rho) is a constant of proportionality and is called the electrical resistivity of the material of the conductor