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## Kalyani's Physics Flashback ### Current Electricity 55. Draw the circuit diagram to show a battery is connected in series with a resistor. 56. A copper wire of 2.5x10-6 m2 cross sectional area that has 8x1028 electrons per metre cubed. 57. 5 cells, each of emf 1.5v are connected in series. C...

## Kalyani's Physics Flashback ### Current Electricity 55. Draw the circuit diagram to show a battery is connected in series with a resistor. 56. A copper wire of 2.5x10-6 m2 cross sectional area that has 8x1028 electrons per metre cubed. 57. 5 cells, each of emf 1.5v are connected in series. Calculate the current across an external resistor added to the series cell combination and calculate the voltage across the added resistor. 58. The potential difference between the ends of a conductor is V. Calculate the current density and conductivity of the conductor if the conductivity is J and the current density is σ respectively. * V/J * σ/J 59. Define the mobility of the charge carriers. 60. The current in a resistor varies with time as shown: I = 5A + 2AS-1t. How many Coulombs of charge flow through a cross section of the resistor between t = 2 and t = 4? 61. What is the dimension of resistance? 62. Calculate the current across the resistor in the following circuit: ``` |---------| | | | I1 | | | I--------> | | | | | I2 | | | |---------| ``` 63. The variation of resistivity with temperature is shown in the following figure. The material is: (Fill in the blanks using conductivity) ### 2015 50. You are given a 1.5V cell and two resistors each of resistance 6Ω and a key. Draw the circuit diagram for the setup when connected to the key to achieve the maximum current in the circuit. 51. The voltmeter reading in the following circuit can be changed by moving a sliding contact B from A to C. Plot a graph to show the variation of the voltmeter reading with the distance of the contact point B from A towards C. ``` |---------| | | | +-------| | | | | | A-----|----B------C | | | | |_______| ``` 51. Apply Kirchhoff's second law to the given circuit and then find the current in the circuit: ``` |---------| | | | R2 |--------> | | I |---------| ^ ^ | | | R1 | | | |_______| ^ ^ | | | ε 1 | | | |_______| ^ ^ | | | R3 | | | |_______| ``` 52. What is the dimension of conductance? 53. The resistance of a metallic wire is 10Ω at 0°C. Calculate the resistance at a temperature of 100°C. Given α = 3.9 × 10-3K-1. 54. A battery of emf Ɛ and internal resistance r is connected to an external resistor R to complete the circuit. Show that the battery delivers maximum power to R when R = r. 46. The drift speed of electrons in a conductor of a circuit is 0.5 mm/s when the potential difference between its ends is 1.5V. What will the drift speed be when the potential difference across it becomes 3V? 47. A copper wire of uniform cross sectional area 1.54×10-6m2 carries a current of 3.08A. Calculate the electric field inside the wire if the resistivity of copper is 1.724×10-8 Ωm. 48. A copper wire and an aluminium wire of the same diameter have their lenghts in the ratio 1:2 and their resistivities in the ratio 5:9. Compare their resistances. 49. * (a) State and explain Ohm's Law * (b) Draw a neat circuit diagram when *n* cells, each of emf *e* and internal resistance *r*, are connected in parallel to an external resistor *R*. Find an expression for the current in the circuit and deduce the conditions necessary for maximum current.