Sure Shot 2016 Electric Current By M K Ezaz

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Ambrose Osborne
5 years ago
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1 Sure Shot 06 Eectric Current B M K Ezaz. A 0 V batter of negigibe interna resistance is connected across a 00 V batter and a resistance of 38 Ω. Find the vaue of the current in circuit. () E 00 0 A: I = = 5A r The pot of the variation of potentia difference across a combination of three identica ces in series, versus current is as shown beow. What is the emf of each ce? () A: Let E be emf of each ce and r be the tota interna resistance of circuit. The equation of termina potentia difference V 3 E Ir () At V = 6V, I = 0. Therefore from eq (), 6 3E 0 E V 3. Two wires of equa ength, one of copper and the other of manganin have the same resistance. Which wire is thicker? () M AM A: since C M and C M but M C AM AC A A The manganin wire is thicker. 4. A resistance is connected across a ce of emf e and interna resistance r. A potentiometer now measures the potentia difference between the terminas of the ce as V. Write the epression for r in terms of E, V and. E V A: r = V 5. Two conducting wires X and Y of same diameter but different materias are joined in series across a batter. If the number densit of eectrons in X is twice that in Y, find the ratio of drift veocit of eectrons in the two wires. () A: In series current is same I X = I Y. For same diameter, cross-sectiona area is same. n eav n eav 6. A conductor of ength L is connected to a dc source of emf V. If this conductor is repaced b another conductor of same materia and same area of cross-section but of ength 3L, how wi the drift veocit v v C n n C

2 change? () ev A: v d ml L When the ength is made 3L, the drift veocit becomes one third. 7. A wire of resistance 8 is bent in the form of a circe. What is the effective resistance between the ends of a diameter AB? () A: Two parts each of resistance 4 are connected in parae; so effective resistance across ends of diameter AB is 8. State and epain with circuit diagram Kirchhoff s rues. (3) A: Kirchhoff s ues: (i) The agebraic sum of currents meeting at an junction is zero, i.e. I = 0 (ii) The agebraic sum of potentia differences across circuit eements of a cosed circuit is zero,i.e., V = 0 9. Write an two factors on which interna resistance of a ce depends. A: The interna resistance of a ce depends on (i) distance () between eectrodes. (ii) area (A) of immersed part of eectrode, and (iii) nature and concentration of eectrote. 0. The foowing graph shows the variation of termina potentia difference V, across a combination of three ces in series to a resistor, versus the current, I. (i) Cacuate the emf of each ce. (ii) For what current I wi the power dissipation of the circuit be maimum? (3) A: (i) Let E be emf of each ce and r be the tota interna resistance of circuit. The equation of termina potentia difference V 3 E Ir () At V = 6V, I = 0. Therefore from eq (), 6 3E 0 E V (ii) At V = 0V, I = A. Therefore from eq (), 0 6 r r 3 (iii) For maimum power dissipation, eterna resistance () = Interna resistance (r) 3E 6 Current, I = = A r 3 3. A conductor of ength is connected to a dc source of potentia V. If the ength of the conductor is doubed b gradua stretching it, keeping V constant, how wi (i) drift speed of eectrons and (ii) resistance of the conductor be affected? Justif our answer. (3) ev A: (i) v d ml L Thus, the ength is doubed, the drift veocit becomes haf. (ii) A When the ength of the conductor is doubed, the area of cross section becomes haf.

3 ' New resistance 4 4 A A Thus, the ength is doubed, resistance becomes four times.. Pot a graph showing temperature dependence of resistivit for a tpica semiconductor. How is this behaviour epained? A: Variation of resistivit with temperature is shown beow: Epanation: In semiconductor the number densit of free eectrons (n) increases with increase in temperature (T) and consequent the reaation period decreases. But the effect of increase in n has higher impact than decrease of ρ. So, resistivit decreases with increase in temperature. 3. (a) You are required to seect a carbon resistor of resistance 47 k Ω ± 0% from a arge coection. What shoud be the sequence of coour bands used to code it? (b) Write the characteristics of manganin which make it suitabe for making standard resistance. () A: (a) Sequence of coour shoud be: Yeow, Vioet, Orange and Siver (b) (i) Ver ow temperature coefficient of resistance. (ii) High resistivit 4. In the given circuit, assuming point A to be at zero potentia, use Kirchhoff s rues to determine the potentia at point B. (3) A: B KCL, current in DC branch I = 3- = A Apping KVL aong path ACDB, V 4 V V V 0 A B B A V 5. (A)Define and derive drift veocit. Write its reationship with reaation time in terms of the eectric fied E appied to a conductor. A potentia difference V is appied to a conductor of ength L. How is the drift veocit affected when V is doubed and L is haved? (5) A: Drift veocit is defined as the average veocit with which the free eectrons get drifted towards the positive end of the conductor under the infuence of an eterna eectric fied appied. It is given b ev v d ml When V is doubed and L is haved, the drift veocit becomes 4 times. (B)Define ionic mobiit. Write its reationship with reaation time. How does one understand the temperature dependence of resistivit of a semiconductor? A: Mobiit of an ion is defined as the drift veocit per unit eectric fied. μ = E v d = m e τ. Its unit is m /Vs.

4 When temperature increases, covaent bonds of neighbouring atoms break and charge carriers become free, so resistivit of semi-conductor decreases with rise of temperature. 6. State the principe of working of a potentiometer. Write two appication.define potentia gradient and derive and write its S.I. unit. (5) A: Principe of potentiometer - When a constant current fows through a wire of uniform crosssectiona area, the potentia drop across an portion of the wire is direct proportiona to the ength of that portion. The fa of potentia per unit ength aong potentiometer wire is caed the potentia gradient. The S.I. unit of potentia gradient is vot/metre. 7. (a)state the principe on which the working of a meter bridge is based. Under what condition is the error in determining the unknown resistance minimized? 5 (b)two students X and Y perform an eperiment on potentiometer separate using the circuit given. Keeping other parameters unchanged, how wi the position of the nu point be affected it (i) X increases the vaue of resistance in the set-up b keeping the ke K cosed and the ke K open? (ii) Y decreases the vaue of resistance S in the set-up, whie the ke K remain open and the ke K cosed? Justif. 8. A: (a)the working of a meter bridge is based on the principe of Wheatstone s bridge. To minimize the error in determining the unknown resistance, the position of baanced point shoud be in the midde of meter-bridge wire. (b) (i) B increasing resistance the current through AB decreases, so potentia gradient decreases. Hence a greater ength of wire woud be needed for baancing the same potentia difference. So the nu point woud shift towards B. (ii) B decreasing resistance S, the current through AB remains the same, potentia gradient does not change. As K is open so there is no effect of S on nu point. 9. (a)state Kirchhoff s rues. (5) A: Kirchhoff s ues: (i) The agebraic sum of currents meeting at an junction is zero, i.e. I = 0 (ii) The agebraic sum of potentia differences across circuit eements of a cosed circuit is zero,i.e., V = 0 (b)cacuate the current drawn from the batter in the given network.

5 A: The equivaent circuit is shown in fig. The five resistors form a baanced Wheatstone s bridge. Since So, is ineffective. The effective resistance of and 5 in series, = + 5 = + = 3 Ω The effective resistance of 4 and 3 in series is = = + 4 = 6 Ω and are in parae. Therefore the Equivaent resistance of network between A and B, ' '' AB ' '' Current drawn from batter, E I '' AB 4 A 0. A wire of 5 Ω resistance is gradua stretched to doube its origina ength. It is then cut into two equa parts. These parts are then connected in parae across a 3 vot batter. Find the current drawn from the batter.(3) A: When the ength of the wire is doubed, the area of cross section becomes haf. ' New resistance A A esistance of each haf part is 30Ω. When both parts are connected in parae, Equivaent resistance = Current drawn from batter, I V eq 3 0.A

Demonstration of Ohm s Law Electromotive force (EMF), internal resistance and potential difference Power and Energy Applications of Ohm s Law

Demonstration of Ohm s Law Electromotive force (EMF), internal resistance and potential difference Power and Energy Applications of Ohm s Law Lesson 4 Demonstration of Ohm s Law Eectromotive force (EMF), interna resistance and potentia difference Power and Energy Appications of Ohm s Law esistors in Series and Parae Ces in series and Parae Kirchhoff