(a) Define volt, the unit of potential difference. (b) Calculate the work done required to move an electron between two points A and B located at a potential difference of 100 V in an electric field.
Electricity
8 topics · about 5 hours · 10% of the paper · asked in 4 of the last papers
Topics in this chapter
- Electric current and the electric circuit
- Electric potential and potential difference
- Ohm's law
- What the resistance of a conductor depends on
- Resistors in series
- Resistors in parallel
- Electric power and commercial units of energy
Board questions from this chapter
19 questions from the CBSE papers we hold.
(i) The given electric circuit is a part of an electrical device. Use the information given in the electric circuit diagram to calculate: (I) Potential difference across the ends of resistor R_2. (II) Value of resistor R_2. (III) Value of resistor R_1. [Circuit data: 12 V source with key K; branch with R_1; a 4.0 Ohm resistor carrying 1.5 A; resistor R_2 in parallel; a 2.0 Ohm resistor; total line current 2.0 A.] (ii) Write the factors on which resistance of a conductor depends and derive the formula for resistance of a given conductor.
A fuse in electric circuit is rated 4 A. Can it be used with an electric heater of rating 2 kW, 200 V? Explain your answer.
(i) How much electric current will an electric iron draw from 220 V source if the resistance of its heating element when hot, is 55 Ohm? Calculate the power consumed by the electric iron when it is operated at 220 V. (ii) In a house, 3 bulbs of 100 watt each, are lit for 5 hours daily and an electric heater of 1.0 kW is used for half an hour daily. Calculate the total energy consumed in a month of 30 days and its cost at the rate of Rs. 3.60 per kWh. (iii) With reason explain, why are alloys commonly used to make elements of electrical heating devices.
Consider the following electric circuit (see figure: a 15 V source, 10 ohm and 15 ohm resistors in parallel, in series with a parallel combination of 60 ohm and 40 ohm resistors, an ammeter A and key K). Calculate the values of the following : (a) The total resistance of the circuit (b) The total current drawn from the source (c) Potential difference across the parallel combination of 10 ohm and 15 ohm resistors.
(a) Write the relationship between resistivity and resistance of a cylindrical conductor of length l and area of cross-section A. Hence derive the SI unit of resistivity. (b) Why are alloys used in electrical heating devices ?
A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.
Define electric power. When do we say that the power consumed in an electric circuit is 1 watt ?
[Case: Domestic mains supply at 220 V between live and neutral wires.] What should be the current rating of the electric circuit (220 V) so that an electric iron of 1 kW power rating can be operated ?
(i) Write the relation between resistance R and electrical resistivity rho of the material of a conductor in the shape of cylinder of length l and area of cross-section A. Hence derive the SI unit of electrical resistivity. (ii) The resistance of a metal wire of length 3 m is 60 ohm. If the area of cross-section of the wire is 4x10^{-7} m^2, calculate the electrical resistivity of the wire. (iii) State how would electrical resistivity be affected if the wire (of part 'ii') is stretched so that its length is doubled. Justify your answer.
Show how you would connect three resistors each of resistance 6 ohm, so that the combination has a resistance of 9 ohm. Also justify your answer.
In the given circuit calculate the power consumed in watts in the resistor of 2 ohm: [circuit diagram shows a 1 ohm resistor and a 2 ohm resistor in series with a 6 V battery]
(i) Define electric power. Express it in terms of potential difference (V) and resistance (R). (ii) An electric oven is designed to work on the mains voltage of 220 V. This oven consumes 11 units of electrical energy in 5 hours. Calculate: (a) power rating of the oven (b) current drawn by the oven (c) resistance of the oven when it is red hot.
In the following diagram, the position of the needle is shown on the scale of a voltmeter. The least count of the voltmeter and the reading shown by it respectively are:
- (a) 0.15 V and 1.6 V
- (b) 0.05 V and 1.6 V
- (c) 0.15 V and 1.8 V
- (d) 0.05 V and 1.8 V [Diagram shows a voltmeter scale from 0 to 3 with 1.5 marked at the top and the needle pointing between 1.5 and 3.]
If four identical resistors, of resistance 8 ohm, are first connected in series so as to give an effective resistance R_s, and then connected in parallel so as to give an effective resistance R_p, then the ratio R_s/R_p is
- (a) 32
- (b) 2
- (c) 0.5
- (d) 16
(a) An electric iron consumes energy at a rate of 880 W when heating is at the maximum rate and 330 W when the heating is at the minimum. If the source voltage is 220 V, calculate the current and resistance in each case. (b) What is heating effect of electric current? (c) Find an expression for the amount of heat produced when a current passes through a resistor for some time.
(a) Three resistors R_1, R_2 and R_3 are connected in parallel and the combination is connected to a battery, an ammeter, a voltmeter and a key. Draw suitable circuit diagram to show the arrangement of these circuit components along with the direction of current flowing. (b) Calculate the equivalent resistance of the following network: [network shown: along line A-C-D-B, R_1 = 5 ohm is between A and C and R_4 = 5 ohm is between D and B; between C and D, R_2 = 10 ohm (upper branch) and R_3 = 10 ohm (lower branch) are in parallel].
(i) Define Electric Power and write its SI unit. (ii) Two bulbs rated 100 W; 220 V and 60 W; 220 V are connected in parallel to an electric mains of 220 V. Find the current drawn by the bulbs from the mains.
(i) State Joule's law of heating. Express it mathematically when an appliance of resistance R is connected to a source of voltage V and the current I flows through the appliance for a time t. (ii) A 5 ohm resistor is connected across a battery of 6 volts. Calculate the energy that dissipates as heat in 10 s.