Electricity Notes PDF

 Charge (Q) 1. Two Types of Charge 2. S.I. Unit of Charge 3. Smallest independent charge  Current (I) 1. Current is Rate of flow of Charge 2. Direction of Current 3. S.I. Unit of Current Q 1. A current of 0.2A is drawn by a de...

 Charge (Q) 1. Two Types of Charge 2. S.I. Unit of Charge 3. Smallest independent charge  Current (I) 1. Current is Rate of flow of Charge 2. Direction of Current 3. S.I. Unit of Current Q 1. A current of 0.2A is drawn by a device for 10 hours. Find the amount of electric charge that flows. (a) 3600 C (b) 4800 C (C) 6000 C (d) 7200 C Q. The filament of an electric lamp draws a current of 0.5 A, which lights for 2 hours. Calculate the Q charge that flows through the circuit. (CBSE 2024) Define Potential Difference. P.D. P.D. between two points is amount of work done in moving a unit charge (1 C) from one point to the other Q. Define S.I. unit of P.D. one volt. Q. Calculate the amount of work done by a cell when 20 C of charge is moved through a P.D. of 3v. (A) 6.66 J (B) 66 J (C) 60 J (D) 0.15 J P.D. is measured by an instrument Voltmeter Q. The expressions that relate (i) Q, I and t and (ii) Q, V and W respectively are (Here the symbols have their usual meanings) (CBSE 2023) Current ka PAPA →Potential Difference (V) [PD] 1.5V Q. Assertion (A) : Electrons move from lower potential to higher potential in a conductor. Reason (R) : A dry cell maintains electric potential difference across the ends of a conductor. (CBSE 2024) (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (c) Assertion (A) is true, but Reason (R) is false. (d) Assertion (A) is false, but Reason (R) is true.  Resistance (R) Metal Atom Metal ion Free electron Conductor Obstruction offered to the flow of charges OR Property of Conductor to obstruct flow of charges  Factors on which Resistance of (Conductor) Depends (i) l (ii) A (iii) Material l – Length (iv) Temperature : A- Area Of Cross Section Q. The resistance of a wire does not depend on its (CBSE 2023) (a) length (b) area of cross-section (c) shape (d) material Q. (i) Write the relation between resistance R and electrical resistivity p of the material of a: conductor in the shape of cylinder of length l and area of cross-section A. Hence derive the : Sl unit of electrical resistivity. (ii) The resistance of a metal wire of length 3 m is 60. If the area of -7 cross-section of the wire is 4 x 10 m2?, calculate the electrical resistivity (CBSE 2024) Q. (a) Write the relationship between electrical resistance and electrical resistivity for a metallic conductor of cylinderical shape. Hence derive the Sl unit of electrical resistivity. ( CBSE 2023) (b) Find the resistivity of the material of a metallic : conductor of length 2m and area of cross-section 1.4 x 10-6m2. The resistance of the conductor is 0.04 ohm.  ? (A) 8 Ω (B) 16 Ω (C) 2 Ω (D) 1 Ω Q. A wire of given material having length ‘l’ and area of cross-section ‘A’ has a resistance of 4. Find the resistance of another wire of the same material having length l/2 and area of cross-section 2A. ( CBSE 2021) A 3A (a) (b) (c) 2A (d) 3A 2 2 Q. In the following figure, three cylindrical conductors A, B and C are shown along with their lengths and areas of cross-section. ( CBSE Term II, 2021-2022) If they are made of same material Find Ra/Rb & Ra/Rc  Resistivity (p) Unit Ωm 1. ρ is a property of the material 2. Metals & Alloys have low ρ (10–8 Ω m to 10–6 Ωm) Good conductor of Electricity Copper & Aluminium are used for transmission lines 3. Insulators like Rubber & Glass have high ρ (1012 Ω m to 1017 Ω m)  OHM’S LAW The Potential difference, V, across the ends of a metallic conductor is directly proportional to the current flowing through it provided its temperature remains the same OHM’S LAW & Experimental setup Q. Let the resistance of an electrical device remain constant, while the potential difference across its two ends decrease to one fourth of its initial value. What change will occur in the current through it? State the law which helps us in solving the above stated question. ( CBSE 2023) ( CBSE 2024) Q. Draw a labelled circuit diagram of the circuit used to show the variation of potential difference across the ends of a resistor with current flowing through it. If you use this circuit, what relation would you find between the voltmeter reading, V and the ammeter reading, I ? ( CBSE 2021) Q. You are provided with a resistor, a key, an ammeter, a voltmeter, four cells of 1.5 V each and few connecting wires. Using these circuit components, draw a labelled circuit diagram to show the setup to study the Ohm's law. State the relationship between potential difference (V) across the resistor and the current (I) flowing through it. Also draw V-I graph, taking V on the X-axis. ( CBSE Term II, 2021-2022)  Combination of Resistors 1. Series : 2. Parallel : Find the equivalent Resistance between X & Y  Combination of Resistors Ye bhi sun le 1. Series : 2. Parallel : Q. If four identical resistors, of resistance 8 ohm, are first connected in series so as to give an effective resistance Rs, and then connected in parallel so as to Rs give an effective resistance Rp, then the ratio R is ( CBSE 2023) p (a) 32 (b) 2 (c) 0.5 (d) 16 Q. The maximum resistance which can be made using four resistors each of 2 Ω is (a) 2 Ω (b) 4 Ω ( CBSE 2020) (c) 8 Ω (d) 16 Ω Q. (a) Write the formula for determining the equivalent resistance between A and B of the two combinations (I) and (ll) of three resistors R1, R2 and R3 arranged as follows : (b) If the equivalent resistance of the arrangements (I) and (11) are Rs and Rp respectively, then which one of the following V—I graphs is correctly labelled ? Justify your answer. ( CBSE Term II, 2021-2022) Q. How you would connect three resistors each of resistance 4 Ω, so that the combination has a resistance of 6 Ω. Q. Show how you would connect three resistors each of resistance 6 Ω, so that the combination has a resistance of 9 Ω. Also justify your answer. ( CBSE 2024) Q. Three 2Ω resistors A, B and C are connected in such a way that the total resistance of the combination is 3 Ω. Show the arrangement of the three resistors and justify your answer. ( CBSE 2020) Disadvantages Of Series Combination 1) If one device fails, all other devices in that series will not work. Eg: Diwali ki lights 2) Devices of different types need different current, for eg a bulb & a heater needs different current & can not be connected in series. This can be done with parallel combination  CIRCUIT DIAGRAM CIRCUIT- Continuous & closed path of electric current. Sl.No. Components Symbols + - 1 An electric cell 2 A battery or a combination of cells + - 3 Plug key or switch (open) ( ) 4 Plug key or switch (closed) ( ) 5 A wire joint 6 Wires crossing without joining Sl.No. Components Symbols 7 Electric bulb 8 A resistor of resistance R 9 Variable resistance or rheostat 10 Ammeter 11 Voltmeter Find 6Ω 2Ω Req Reading of Ammeter 3Ω P.D. in all resistors 1Ω Current in all resistors _ + 15v Find 6Ω 2Ω Req Reading of Ammeter 3Ω P.D. in all resistors 1Ω Current in all resistors _ + 15v Q. In the given circuit determine the value of : (i) total resistance of the circuit ( CBSE Term II, 2021-2022) (ii) current flowing through the ammeter. Q. Find the current flowing through the following ( CBSE 2024) Draw a schematic diagram of a circuit consisting of a battery of four 1.5 V cells, a 5 Ω resistor, a 10 Ω resistor and a 15 Ω resistor and a plug key, all connected in series. Now find (I) The electric current passing through the circuit, and (I) Potential difference across the 10 Ω resistor when the plug key is closed. ( CBSE 2024) (a) Find the value of total resistance between the points A and B. (b) Find the resistance between the points Band C. ( CBSE 2024) (c) (i) Calculate the current drawn from the battery, when the key is closed. OR (c) (ii) In the above circuit, the 16 Ω resistor or the parallel combination of two resistors of 8 Ω, which one of the two will have more potential difference across its two ends? Justify your answer. ELECTRIC POWER Rate at which Electrical Energy is consumed ( CBSE 2024) Q. In the given circuit calculate the power consumed in watts in the resistor of 2 Ω. ( CBSE 2024) Q. An electric heater rated 1100 W operates at 220 V. Calculate (i) its resistance, and (ii) the current drawn by it. ( CBSE Term II, 2021-2022) Q. Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1 A. The current through the 40 W bulb will be (a) 0.4 A (b) 0.6 A (c) 0.8 A (d) 1 A ( CBSE 2020) Q. Two LED bulbs of 10 W and 5 W are connected in series. If the current flowing through 5W bulb is 0.005A, the current flowing through 10W bulb is : (a) 0.02 A (b) 001 A ( CBSE 2023) (c) 0.005 A (d) 0.0025 A Electrical Energy (E) An electric kettle of 2KW is used for 2h. Calculate Energy Consumed in KWh & Joules. ( CBSE Term II, 2021-2022) Calculate Electrical Energy in KWh & Joules 100W 100W 100W 10h per day for 30 days Bijli ka Bill banao Q. For a heater, rated 4 kW and 220 V, calculate the following : (a) Energy consumed in 2 hours (b) If 1 kWh is priced at ₹4.50, then the cost of energy consumed. ( CBSE Term II, 2021-2022) Q. In a house, 2 bulbs of 50 W each are used for 6 hours daily and an electric geyser of 1 kW is used for 1 hour daily. Calculate the total energy consumed in a month of 30 days and its cost at the rate of ₹8.00 per kWh. ( CBSE 2023) ( CBSE 2020)  HEATING EFFECT OF ELECTRIC CURRENT When an electric current passes through a conductor or an electric device , the conductor becomes hot after some time and produces heat. This is called heating effect of Electric Current. BULB FAN TOASTER MOBILE PHONE Joule’s Law Of Heating ✓ Heat produced in a resister R i (t) PRACTICAL APPLICATION OF HEATING ELLECT OF ELECTRIC CURRENT IRON ELECTRIC OVEN ELECTRIC KETTLE TOASTER Q. Assertion (A): Alloys are commonly used in electrical heating devices like electric iron and heater. Reason (R) : Resistivity of an alloy is generally higher than that of its constituent metals but the alloys have low melting points then their constituent metals. (a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A). (b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion (A). (c) (A) is true, but (R) is false. (d) (A) is false, but (R) is true. (2020) ( CBSE 2020)  ELECTRIC BULB Filament Tungsten (High Melting Point) Filament is Heated & it emits light. Most of Energy consumed appears as heat, only small part as light Tungsten has very high Melting point.  ELECTRIC FUSE – Safety Device Electrical fuse is used to prevent short circuit. Fuse has low melting point so when high current passes through it melts and stop the flow of current. Appliance Fuse wire in series with the appliance Fuse wire - Alloy of Al, cu, lead, Iron Fuse Wire should have -:  Application of heating effect Rating of Fuse Wire – Max Current Q. State Joule's law of heating. How is this effect useful in electric circuits where fuse is used as a safety device? ( CBSE 2024) Q. An electric kettle consumes 1 kW of electric power when operated at 220 V. The minimum rating of the fuse wire to be used for it is ( CBSE 2023) (a) 1A (b) 2A (c) 4 A (d) 5 A  Define S.I unit Of Current 1 Ampere. If one coulomb of charge flows through a conductor in one second, the current flowing through the conductor is known as one ampere Define S.I unit Of Potential Difference 1 Volt. The potential difference between two point is said to be 1 volt if 1 Joule of work is done in moving a positive change of 1 Coulomb from one point to the other.  Define S.I unit Of Resistance 1 Ohm One ohm is defined as that resistance of an object when a current of 1 Ampere flows through an object on applying Potential difference of 1V Define S.I unit Of Power 1 Watt 1 Watt is the Power Consumed in a circuit when 1 Ampere of Current Flows on applying a Potential difference 1Volt.