SUBJECT : PHYSICS - SSA Punjab

16. Three capacitors of capacitance C 1 , C 2 , C 3 are connected in (i) series (ii) parallel.Find the expression for resultant capacitance.17. Derive the expression for capacitance of parallel plate capacitor when dielectricslab is inserted between plates of the capacitor.18. Derive the expression for capacitance of parallel plate capacitor when conductingslab is inserted between plates of the capacitor.19. Give the principle, construction and working of Vande Graff generator.Unit II: Current Electricity2 marks questionsCURRENT ELECTRICITY1. How does the drift velocity of electrons in a metallic conductor vary withincrease in temperature?2. What are ohmic and non ohmic devices? Give one example of each.3. Define resistance. On what factors it depends?4. Draw a graph to show the variation of resistance of a metal wire as afunction of its diameter, keeping length and temperature constant.5. Define resistivity. On what factors it depends.6. Resistivities of copper, silver and mangnin are 1.7×10 -8 Ωm, 1.0 ×10 -8 Ωmand 44×10 -8 Ωm respectively. Which of these is the best conductor?7. A metal and a semiconductor material are cooled. What happens to theirconductivities and why?8. What is difference between e.m.f and terminal potential difference?9. Name the material used for making standard resistors? Give two reasons.10. What happens to the drift velocity (v d ) of electrons and to the resistance R iflength of a conductor is doubled (keeping potential difference unchanged)?11. The V-I graph is drawn for a metal wire at two temperature T 1 and T 2 . IfT 1 >T 2 , draw the graph.12. A large number of free electrons are present in metals. Why is there nocurrent in the absence of electric field across it?13. What is more dangerous to human body, the current or voltage?14. It is found that 10 20 electrons each having a charge of 1.6 ×10 -19 C, pass froma point X towards another point Y in 0.1 s. What are the current and itsdirection?15. An electric motor operating on a 50 V dc supply draws a current of 12 A. Ifthe efficiency of the motor is 30%, estimate the resistance of the windings ofthe motor.16. Will water flow more easily through a wide pipe or a narrow pipe? Willcurrent flow more easily through a thick wire or a thin wire?17. Distinguish between a kilowatt and a kilowatt-hour.36