Conductor- Insulator: Materia Materials through which electric current cannot pass are called insulators. Electric Circuit: A continuous a CLASS X- ELECTRICITY als through which electric current can pass are called conductors and closed path of an electric current is called an electric circuit Components of electric current: 4 components Cell to produce electricity Wire To carry electric current Switch To control electricc current Bulb ( appliance) to use electric current Types of Charges: Two types Positive Charge and Negative Charge Positive Charge Charge acquired by a glass rod when rubbed with silk is called positive charge Negative Charge The charge acquired by an ebonite rod when rubbed with a wool is called negative charge. Static Electricity : deals with the electric charge at rest. Current Electricity deals with electric charges in motion. Coulomb s Law Coulomb's law states that: The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them. The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different sign, the force between them is attractive. Coulomb's law can also be stated as a simple mathematical expression Coulomb --. Si unit of charge. One coulomb is defined as the charge which repels and equal and similar charge with a force of 9 x 10 9 N when placed in vacuum at a distance of 1 meter from it. One coulomb is the charge contained by 6 x 10 18 electrons Charge of an electron = -1.6 x10-19 coulomb Repulsion & Attraction Like charges repel and unlike charges attract. Direction of electric Current 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. Electric current is expressed by the amount of charge flowing through a particular area in unit time. Electric current is the rate of flow of electric charges 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
SI unit of Electric Current is called ampere (A), Definition of ampere: One ampere is constituted by the flow of one coulomb of charge per second, that is, 1 A = 1 C/1 s. Small quantities of current are expressed in milliampere (1 ma =10-3 A) or in microampere (1 A = 10-6 A) Electric Field : the region around a charged body within which its influence can be detected Ammeter instrument used to measure the electric current Ammeter is always connected in series in a circuit A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit. Current, I = 0.5 A; Time, t = 10 min = 600 s. Q = It = 0.5 A 600 s = 300 C 1. The filament of an electric lamp draws a current of 0.4 A which lights for 3 hours. Calculate the amount of charge that flows though the circuit. ( I = Q/t) Current I == 0.4 A Time, t = 3 hours = 3 x 60 x 60 = 10800 s Charge Q = I x t = 0.4 x 10800 = 4320 C 2... n electrons flow through a cross section of a conductor in time t. If the charge of an electron is e, write an expression for the current in the conductor. Q = ne I = ne / t 3. A conductor carries a current of 0.2 A. Find the amount of charge that will pass through the cross section of the conductor in 30 s. How many electrons will flow in this time interval if the charge on one electron is 1.6 x 10-19 C? Current I = 0.2.A Time, t = 30 s Q = I x t = 0.2 x 30 = 6 C Charge of an electron, e = 1.6 x 10-19 C Charge, Q = 6 C
Q = ne n = Q/ e = 6 / 1.6 x 10-19 C = 3.75 x 10 19 ELECTRIC POTENTIAL / POTENTIAL DIFFERNECE The electric potential difference between two points in an electric circuit carrying current is defined as the work done to move a unit charge from one point to the other Potential difference (V) between two points = Work done (W) / Charge (Q) V = W/Q volt The SI unit of electric potential difference is volt (V Definition of one volt 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. 1 volt = 1 joule / 1 coulomb 1 V = 1 J C 1 Voltmeter Device used to measure the potential difference. The voltmeter is always connected in parallel across the points between which the potential difference is to be measured. Role of cell in a circuit The chemical action within a cell generates the potential difference across the terminals of the cell, even when no current is drawn from it. When the cell is connected to a conducting circuit element, the potential difference sets the charges in motion in the conductor and produces an electric current. In order to maintain the current in a given electric circuit, the cell has to expend its chemical energy stored in it. ( emf) How much work is done in moving a charge of 2 C across two points having a potential difference 12 V? Potential difference, V = 12 V Charge, Q = 2C. V = W/ Q Work done W = VQ = 12 V 2 C = 24 J. Circuit diagram is a schematic diagram, in which different components of the circuit are represented by the symbols. Symbols of commonly used components OHM S LAW states 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.
V I V/I = constant = R or V = IR R is a constant for the given metallic wire at a given temperature and is called its resistance. RESISTANCE ( R) The resistance of a conductor is the ratio of the potential difference across its ends to the strength of the current passing through it. Resistance = Potential difference / Current Plotting a V/I graph and its interpretation Current I Potential V / I R difference- V 0.1 0.4 0.4 /0.1 = 4 4Ω 0.2 0.8 0.8 / 0.2 = 4 4Ω 0.3 1.2 1.2 / 0.3 = 4 4Ω 0.4 1.6 1.6 / 0.4 = 4 4Ω Plot current (A) in X axis Plot Potential Difference (V) in Y axis Slope of the V-I graph represents Resistance. ( Slope of a graph means y/ x) Plotting a I/V graph and its interpretation Current I Potential I / V R= 1/I/V difference- V 0.1 0.4 0.1/0.4 = 0.25 1/0.25= 4Ω 0.2 0.8 0.2/0.8 = 0.25 1/0.25= 4Ω 0.3 1.2 0.3 / 1.2 = 0.25 1/0.25= 4Ω 0.4 1.6 0.4/1.6 = 0.25 1/0.25= 4Ω Plot current (A) in Y axis Plot Potential Difference (V) in X axis Reciprocal of the Slope of the I / V graph represents Resistance. Resistance is the property of a conductor to resist the flow of charges through it. SI Unit of Resistance ohm, represented by the Greek letter Ω Definition of 1 ohm 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 is 1Ω. That is, 1 ohm = 1 volt / 1 ampere
Effect on Current when resistance is doubled I = V/R, The current through a resistor is inversely proportional to its resistance. If the resistance is doubled the current gets halved Factors on which Resistance depend 1. Size of the conductor 2. Nature of the material 3. Temperature of the conductor Variable Resistance A component used to regulate current without changing the voltage source is called variable resistance.. Rheostat a device in an electric circuit used to change the resistance