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Ashok0210

Asked: February 23, 2021In: Class 12 Physics

Answer the following questions: (a) A steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor: current, current density, electric field, drift speed? (b) Is Ohm’s law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ohm’s law. (c) A low voltage supply from which one needs high currents must have very low internal resistance. Why? (d) A high tension (HT) supply of, say, 6 kV must have a very large internal resistance. Why?

Class 12 Physics CBSE and UP Board Current Electricity Additional Exercise Chapter-3 Exercise 3.18 NCERT Solutions Class 12 Physics Chapter 3 Question 18

Ashok0210

Asked: February 23, 2021In: Class 12 Physics

What conclusion can you draw from the following observations on a resistor made of alloy manganin?

Class 12 Physics CBSE and UP Board Current Electricity Additional Exercise Chapter-3 Exercise 3.17 NCERT Solutions Class 12 Physics Chapter 3 Question 17

Ashok0210

Asked: February 23, 2021In: Class 12 Physics

Two wires of equal length, one of aluminum and the other of copper have the same resistance. Which of the two wires is lighter? Hence explain why aluminum wires are preferred for overhead power cables. (ρAl = 2.63 × 10⁻⁸ Ω m, ρCu = 1.72 × 10⁻⁸Ω m, Relative density of Al = 2.7, of Cu = 8.9.)

Class 12 Physics CBSE and UP Board Current Electricity Additional Exercise Chapter-3 Exercise 3.16 NCERT Solutions Class 12 Physics Chapter 3 Question 16

Ashok0210

Asked: February 23, 2021In: Class 12 Physics

(a) Six lead-acid type of secondary cells each of emf 2.0 V and internal resistance 0.015 Ω are joined in series to provide a supply to a resistance of 8.5 Ω. What are the current drawn from the supply and its terminal voltage? (b) A secondary cell after long use has an emf of 1.9 V and a large internal resistance of 380 Ω. What maximum current can be drawn from the cell? Could the cell drive the starting motor of a car?

Class 12 Physics CBSE and UP Board Current Electricity Additional Exercise Chapter-3 Exercise 3.15 NCERT Solutions Class 12 Physics Chapter 3 Question 15

Ashok0210

Asked: February 23, 2021In: Class 12 Physics

The earth’s surface has a negative surface charge density of 10⁻⁹ C m⁻². The potential difference of 400 kV between the top of the atmosphere and the surface results (due to the low conductivity of the lower atmosphere) in a current of only 1800 A over the entire globe. If there were no mechanism of sustaining atmospheric electric field, how much time (roughly) would be required to neutralise the earth’s surface? (This never happens in practice because there is a mechanism to replenish electric charges, namely the continual thunderstorms and lightning in different parts of the globe). (Radius of earth = 6.37 × 10⁶ m.)

Class 12 Physics CBSE and UP Board Current Electricity Additional Exercise Chapter-3 Exercise 3.14 NCERT Solutions Class 12 Physics Chapter 3 Question 14

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