Formatting page ...
Prelim -I, 2020-21 Class: X Duration: 2hrs Subject: Physics Max. Marks: 80 Section I is compulsory. Attempt any four questions from Section II. The intended marks for questions or parts of questions are given in brackets [ ]. SECTION A (40 Marks) Attempt all questions from this Section. Question 1 a) Why can a machine not be 100 % efficient? [2] b) If the power of a motor is 60 KW, at what speed can it raise a load of 14000 N? [2] c) a) Define radioactivity. b) During the emission of beta particle, the __________number remains the same. [2] d) e) A nut is opened by a wrench of length 20 cm. If the least force required is 2 N, find the moment of force needed to loosen the nut. A large number of free electrons are present in metals. Why is there no current in the absence of electric potential across it? [2] [2] Question 2 a) b) c) d) e) What is the relationship between the mechanical advantage and velocity ratio for : a) an ideal machine b) a practical machine On what factors does the position of the Centre of gravity of the body depend? A machine can open a nut by applying a force of 120 N while using the lever handle of length 50 cm. How long handle is required if he wants to open it by applying force of only 40 N a) Name the radiations which are absorbed by greenhouse gases in the earth s atmosphere. b) A radiation X is focused by a particular device on the bulb of a thermometer and mercury in the thermometer shows the rapid increase. Name the radiation X. What is earthling? What is its use? [2] [2] [2] [2] [2] Question 3 a) b) c) What energy changes that take place in the following: a) a photovoltaic cell b) a microphone Define quality of a sound. What does it depend on? Name two factors on which the heat absorbed or given out by a body depends. [2] [2] [2]
|
