19. Consider the junction diode as ideal. The value of current flowing through AB is: 1k a www +4 V -6V (a) OA (b) 10A (d) 10 A (c) 10'A 20. The temperature dependence of resistances of Cu and undoped SI in the temperature range 300 - 400 K is best described by: (a) Linear increase for Cu, linear increase for Si. (b) Linear increase for Cu, exponential (a) a and B both are negative (b) a is positive and B is negative (c) a and B both are positive (d) a is negative and B is positive 25. If a battery of 6 V is connected terminals of 3 m long wire of thíckness and resistance of the 100 2. The difference of potential be the two points separated by 50 cm 31. increase for Si. (c) Linear increase for Cu, exponential decrease for Si. (d) Linear decrease for Cu, linear decrease for St. wire will be (a) 1 V (c) 2 V (b) 1.5 V (d) 3 V 21. When 5 V potential difference is applied across a wire of length 0.1 m, the drift speed of electrons is 2.5 x 10 ms. If the electron density in the wire is 8 x 10 m, the resistivity of the material is close to: (a) 1.6 x 10 a m (b) 1.6 x 10 am (c) 1.6 x 102 m (d) 1.6 x 102 m 26, A wire of resistance 4Q is stretche twice its original length. The resistar stretched wire would be (a) 20 (c) 82 (b) 42 (d) 16 2 22. A current 4.0 A exists in a wire of cross- sectional area 2.0 mm. If each cubic metre of the wire contains 12.0 x 10 free electrons, then the drift speed is (a) 2x 10 ms (b) 0.5 x 10ms (c) 1.04 x 10ms (d) None of these 27. The electrical conductivity of the m decreases with temperature, because (a) the energy of the electrons incre with temperature (b) a metal expands on heating (c) the atoms of the metal vibrate mon higher temperature (d) metals have low specific heat 28. If a wire is stretched to make it 0.1% loy its resistance will 23. Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1.0 mm and conductor B is a hollow tube of outside diameter 2.0 mm and inside diameter 1.0 mm. Find the resistance ratio R/R measured between their ends. (a) increase by 0.2% (b) decrease by 0.2% (c) decrease by 0.05% (d) increase by 0.05% 29. Two wires A and B of the same mal (a) 3 (b) 2 id) 0 5