Electricity Past Paper Exam Questions PDF

## ALAKH SIR ke FARREY - ELECTRICITY ### CHARGE (Q): * Two types of charges: Positive (+) and Negative (-) * SI unit of charge: Coulomb (C) * Smallest independent charge: Electron (e) * 1e = $1.6 \times 10^{-19}$C * (-,-) $\rightarrow$ Repel * (+, -) $\rightarrow$ Attract *...

## ALAKH SIR ke FARREY - ELECTRICITY ### CHARGE (Q): * Two types of charges: Positive (+) and Negative (-) * SI unit of charge: Coulomb (C) * Smallest independent charge: Electron (e) * 1e = $1.6 \times 10^{-19}$C * (-,-) $\rightarrow$ Repel * (+, -) $\rightarrow$ Attract * Diagram: Depicts the flow of electrons and conventional electric current direction ### CURRENT (I): * Current is the rate of flow of charge * Direction of current: Opposite to the direction of electron flow * SI unit of current: Ampere (A) $I = \frac{Q}{t}$ , $Q = It$ ### POTENTIAL DIFFERENCE (P. D) \[V]: * Potential Difference between two points is the amount of work done in moving a unit charge (1C) from one point to the other. * Units: Volts (V) or Joules per Coulomb (J/C) $V = \frac{W}{Q}$ , $W = QV$ * Potential difference is measured by a Voltmeter * Electric current (A) is measured by an Ammeter. * Diagram: A battery with terminals labeled H.P. (High Potential) and L.P. (Low Potential) * Electrons flow from lower potential to higher potential. * Current flows from Higher potential to lower potential. * Symbol: Depicts a combination of cells to form a battery (e.g., four 1.5V cells in series to give 6V). ### RESISTANCE: * Obstruction offered to the flow of charges (current) * Property of a conductor to obstruct flow of charges. $Q = It$ , $W = QV$ * Diagram: A conductor with labeled current (I), length (J), and area of cross-section (A) * Formula: $R = \rho \frac{l}{A}$ in Ohms ($\Omega$) * Factors on which Resistance of a conductor depends: * Length (l): R $\propto$ l * Area (A): R $\propto$ $\frac{1}{A}$ * SI unit of R: $\Omega$ - ohm ### Material resistivity ($\rho$) * Formula: $\rho$: $R = \rho \frac{l}{A}$ * SI unit = $\Omega$m * $\rho$ is a property of the material. * Metals and Alloys have low $\rho$ (Good conductors of electricity; e.g., copper and aluminum are used for transmission lines). * Insulators like Rubber and Glass have high $\rho$. --- ### OHM'S LAW: * The potential difference (V) across the ends of a metallic conductor is directly proportional to the current (I) flowing through it, provided its temperature remains the same. * $V \propto I$ (Temperature constant) * $V = IR$ , Where R is the resistance in ohms * V = Volt * I = Ampere * Diagram: The graph of Voltage vs Current in the linear region is a straight line that passing orgin * Trick - VIRal * V=IR * Experimental Set up: Diagram shows circuit diagram that includes plug key, ammeter, voltmeter, unknown Resistance or Resistor ### Combination of Resistors: 1) **Series** * I (current) is same * V (Voltage) is Different $R_e = R_1 + R_2 + R_3$ 2) **Parallel** * I (current) is Different * V (Voltage) is same $\frac{1}{R_e}$ = $\frac{1}{R_1}$ + $\frac{1}{R_2}$ + $\frac{1}{R_3}$ ### Disadvantage of series combination (1) if one device fails, all others devices in that series will not work. (2) Devices of different types need different current, for eg a bulb and heater needs different current and cannot 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 | $\dashv \vdash$ | | 2 | A battery or a combination of cells | | | 3 | Plug key or switch (open) | | | 4 | Plug key or switch (closed) | | | 5 | A wire joint | $\Longleftrightarrow$ | | 6 | Wires crossing without joining | | | 7 | Electric bulb | | | 8 | A resistor of resistance R | www | | 9 | Variable resistance or rheostat | | | 10 | Ammeter | A | | 11 | Voltmeter | | --- ### Electrical Energy (E) * supplied by cell * Generally: E $\implies$ S.I unit $\implies$ Joules * 1Kwh = $3.6 \times 10^6$J * But, generally E is measured in KWh $E = P \times t$ , (t $\implies in \, hour$) k w h = $\frac{watt}{1000}$ ### Bijlika Bill Bango * Energy ka Paisa * Electric Meter $\implies 1 \, unit \, of \, energy$ * $1 \, unit = 1 kWh$ * $Bill = no \, of \, units \times price \, of \, unit$ * Energy in kwh * (kitni energy Use ki kwh mein) * ### 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 produce heat. This is called Heating effect or electric current. #### Practical Application of Heating Effect of electric current By selecting alloys $\implies$ ex- bulb, toaster, mobile phone, fan $\implies High \, resistivity, \, Heat \uparrow$, $\implies High \, Melting \, point$ $\implies$ Do not oxide $H$ is proportional to the square of intensity, Resistance and time $H = i^2Rt$ [Joule's law of Heating] * Joule's law of Heating $H \propto i^2$, $H \propto R$, $H \propto t$ ### Electric Bulb * filament $\implies\,Tungsten \,(High\,melting\, Point)\, is\, Heated\, and \,it\, emits\, light. * Most of energy consumed Pure Resister appears as heat, only small part qs 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. * Fuse wire in series with the appliance. * Fuse wire $\implies Alloys \, of \,Al, Cu,Lead, \,iron$ Appliance current $\implies\,max$ Fuse wire should have $\implies High \,resisitivity, \,low \, melting \,point.$ if high current flows (more than required), Fuse wire gets heated and melts. Rating of fuse $\implies\,1A, 2A,3A, 4A,5A, 10A \,etc$ Rating of fuse wire $\implies\,max \,current$ ### Electric Power * Rate at which electrical Energy is consumed. $P=Vi$ Ampere * $V = IR$ * $P=i^2R$ * $P=\frac{V^2}{R}$ --- ### CURRENT YEARS QUESTIONS **QUESTION-1**: i) An electric lamp filament draws a current of 0.5A and operates for 2 hours. Calculate the charge that flows through the circuit. ii) If an electric source supplies a charge of 500 Coulombs and a device draws a current of 25 mA, determine the time required for the source to be completely discharged. (CBSE 2024) **QUESTION-2**: i) The values of current (I) flowing in a given resistor for the corresponding values of potential difference (V) across the resistor are given in the following. a) Plot a graph between V and I. b) Calculate the resistance of the resistor with the help of the graph. ii) Pick up, for three samples of nichrome wire with Resistance R1, R2 and R3 choose from the following that holds true for this graph. a) $R1=R2=R3$ b) $R1 > R2 > R3$ c) $R3>R2>R1$ d) $R3>R2>R1$ (CBSE 2023,2024) **QUESTION-3**: i) Three cylindrical conductors A, B and C are shown along with their lengths and areas of cross-section. (CBSE 2021, 2022, 2024) (CBG)\\ If these three conductors are made of the same material and RA, RB and RC are their respective resistances, then find (i) $R_A$ / $R_B$ (ii) $R_A$ / $R_C$. \\ ii) The resistance of a metal wire of length 3m is 6 $\Omega$. If the area of cross-section of the wire is $4 \times 10^{-7} m^2$, calculate the electrical resistivity of the wire.\\ State how would electrical resistivity be affected if the wire (of part ii) is stretched so that its length is doubled. Justify your answer. **QUESTION-4**: i) A 6 $\Omega$ resistance wire is doubled on itself. calculate the new resistance of the wire. ii) Three 2 $\Omega$ resistors A, B and c are connected in such a way that the total resistance of the combination is 3 $\Omega$ show the arrangement of the three resistors and justify your answer. CBSE (2016,2020,2023) **QUESTION-5**: i) state Joule's law of heating. Express it mathematically when an applience of resistance R is connected to a source of voltage V and the current/Flows through the appliance for time t. ii) A 5 $\Omega$ resistor is connected across a battery of 6 Volts. Calculate the energy I that dissipates as heat in 10 s. (CBSE 2021,2022,2024) **QUESTION-6**: Define electric power and state its SI unit. The commercial unit of electrical energy is known as 'unit'. Write the relation between this unit' and Joule. In a house, 2 bulbs of 50w each are used for 6 hours daily and electric geyser of 1kW is used for 1 hour daily. Calculate the total energy consumed in a month of 30 days and it cost at the rate of 8.00 per kWh. Two bulb rated 100W; 220V and 60 W: 220V are connected in parallel to an electric mains of 220V. Find the current drawn by the bulbs from the main. (CBSE 2020,2024) **QUESTION-7**: Which type of circuits-series or parallel, should be used when you have to operate different electrical gadgets in your house? List two reasons for your answer. (CBSE 2020,2024) --- **QUESTION-8**: A student wants to use an electric heater, an electric bulb and an electric fan simultaneously How should these gadgets be connected with the mains? Justify your answer by giving three reasons. In the circuit given below, the resistors R1, R2 and R3 have the values 10Ω, 20Ω and 30Ω respectively, which have been connected to a battery of 12V. Calculate (a) the current through each resistor (b) the total circuit resistance, and (c) the total current in the Circuit.(CBSE 2019.2021,2022) \\ **QUESTION-9**: study the following electric circuit in which the resistors are arranged in three arms A, B and c a) Find the equivalent resistance of arm A. b) Calculate the equivalent resistance of the parallel combination of the arms B and c. Determine the current that flows through the ammeter. Determine the current that flows in the ammeter when the arm B is withdrawn from the circuit. (CBSE 2021,2022)CBQ **QUESTION-10**: i) Write the formula for determining the equivalent resistance between A and B of the two combinations (I) and (II) of three resistors R1, R2 and R3 arranged as follows (1) ii) if the equivalent resistance of the arrangements (I) and (II) are Rs and Rp respectively, then which one of the following V - I graphs is correctly labelled? (CBSE 2021,2022) **QUESTION-11**: i) How much current will an electric iron draw from a 220V source if the resistance of its element when hot is 55 ohms? Calculate the wattage of the electric iron when it operates on 220 Volt. (ii) The potential difference across the two ends of a circuit component is Decreased to one-third of its initial value, while its resistance remains Constant. What change will be observed in the current plowing through it? Name and state the law which helps us to answer this question. Draw a schematic diagram of a circuit consisting of a battery of four 1.5V cells, as Ω resistor, a resistors. All connected in series. Now find The electric current passing through the circuit, and Potential difference across = the 10 resistors. a plug Key When the plug hey is closed? (CBSE 2016,2019,2020,2024)