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11th Class Chapter four Physics Short Questions

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Question: 1
What do you mean by variable force?Give its two examples?
Answer: 1
1-47
The force which is not constant but varies in magnitude and direction or in both is called a variable force.
  1. Force a gravity acting on a rocket moving away from earth.
  2. Force exerted by the spring increases by the amount of stretch.
Question: 2
Define work and its SI unit.
Answer: 2
2-47
Alternate Text
Question: 3
Define conservative field.Give its example.
Answer: 3
3-47
Conservative Field: The field in which work done along a closed path is zero is called conservative field.For example, Earth's Gravitational field
Question: 4
Show that 1 kWh = 3.6x106J

Answer: 4
4-47
As
1 kWh=1000 Wx 3600 s
1 kWh =3600000 j
1 kWh = 3.6x106 j
Question: 5
When a rocket re enters the atmosphere, its nose con becomes very hot.Where does this heat energy come from?
Answer: 5
5-47
The atmosphere of earth contains a large number of dust particles,gases and water vapours.So when a rocket enters into the atmosphere and passes through these particles, due to the force of friction, the kinetic energy of the rocket is lost in the form of heat. That's why its nose cone becomes very hot.
Question: 6
Define kilowatt hour (kWh).
Answer: 6
6-47
Kilowatt hour is the work done in one hour by an agency whose power is one kilowatt.
1 kWh = 3.6x106
Question: 7
Define conservative and non-conservative fields?
Answer: 7
7-47
Conservative field: The field in which work done along a closed path is zero is called conservative field. For Example, Earth's gravitational field

Non-Conservative fields:The field in which work done along a closed path is not zero is called non-conservative field. For Example, field of frictional force.
Question: 8
What are the essential conditions for conservative field?
Answer: 8
8-47
For a field to be conservative, energy should be conserved and work should be independent of the path followed.As in case of work done along a path in the gravitational field of earth.
Question: 9
What is geothermal energy? How is it generated ?
Answer: 9
9-47
The heat energy extracted from inside the Earth in the form of steam or hot water is called geothermal energy.
It can be generated by the following processes
  • Radioactive Decay
  • Residual Heat of Earth
  • Compression of Material
Question: 10
A person holds a bag of groceries while standing still. A car is stationary with its engine running.How are the two situations similar from the point of view of work ?
Answer: 10
10-47
In both the above two cases, since there is no displacement, therefore the work done will be zero. Hence in this respect, the two situation are similar.
Question: 11
What sort of energy is in the following?
  1. A Moving Car
  2. A Compressed Spring
Answer: 11
11-47
A Moving car has kinetics energy .
A Compressed Spring has elastic potential energy.
Question: 12
Differentiate between conservative and non- conservative force.
Answer: 12
12-47
Conservative Force: The force by which work done along a closed path is zero is called conservative force. For Example, gravitational force, electric force and magnetic force.

Non-Conservative Force: The force by which work done along a closed path is not zero is called non-conservative force. For example,frictional force, air resistance and normal force.
Question: 13
An object has one joule of potential energy.Explain what it means.
Answer: 13
13-47
It means that work has been done on the body by the force of 1 N which has lifted the body through a distance of 1 m.This work has been stored in the body in the form of P.E. Which is 1J.
Question: 14
What sort of energy is in the following?
(A) Compressed spring (b) Water in high dam
Answer: 14
14-47
a) A compressed spring has Elastic Potential Energy stored in it.
B) Water in a high dam has Gravitational potential Energy in it.
Question: 15
Name some non- conventional energy sources.
Answer: 15
15-47
Some of the non-conventional energy sources are:
  • Energy from tides
  • Energy from waves
  • Energy from biomass
  • Energy from waste products
  • Solar Energy
  • Geothermal Energy
Question: 16
How can you get energy from the waves?
Answer: 16
16-47
The tides and winds blow across the surface of ocean due to which strong water waves are produced. Professor Salter invented a devices called Salter's duck.It has two parts: duck float and balance float. The wave energy produces the movement in duck float relative to balance float. The relative motion of duck float can be used to run electricity generators.
Question: 17
Explain briefly about residual heat of the earth.
Answer: 17
17-47
Hot igneous rocks within 10km of earth's surface are present in molten form They conduct heat energy from interior part of the earth. The temperature of these rocks is 200° C or more.
Question: 18
How can we gain energy from tides?
Answer: 18
18-47
The tides raise the water in the sea roughly twice a day.If the water at the high tides is trapped in a basin by constructing a dam, then it is possible to use this as a source of energy. There dam is filled at high tide and water is released in a controlled way at low tide to drive the turbines and generate electricity.
Question: 19
A boy uses a catapult to throw a stone which accidentally smashes a greenhouse window.What energy changes are involved?
Answer: 19
19-47
Initially, the catapult had elastic P.E when the stone is thrown, its P.E is converted into K.E On striking the window, this energy is converted into sound energy, heat energy work done in breaking the window into pieces and kinetic energy of pieces.
Question: 20
How many most common methods can be used for the conversion of biomass into fuel? Write their names.
Answer: 20
20-47
There are two methods for conversion of biomass into fuel:
  • Direct Combustion Method
  • Fermentation Method
Question: 21
What are non-conventional energy sources? Describe briefly.
Answer: 21
21-47
The energy sources which are not very common theses days are called non- conventional energy sources. Some of the non-conventional energy sources are :
  1. Energy from tides
  2. Energy from waves
  3. Energy from biomass
  4. Energy from waste products
  5. Solar Energy
  6. Geothermal Energy
Question: 22
A girl drops a cup from a certain height which breaks into pieces.What energy changes are involved?
Answer: 22
22-47
When the cup was in the hands of girl, it had gravitational P.E when the cup is dropped, its P.E. Is converted into the K,E On striking the ground , this energy is converted into sound energy, heat, work done in breaking the cup into pieces and kinetic energy of pieces.
Question: 23
How energy is obtained from direct combustion and fermentation.
Answer: 23
23-47
Direct Combustion: It is applied to get energy from waste product commonly known as solid waste and confined it into chamber and ignite it.The heat produced is then used in a boiler to run the turbine of generator

Fermentation: Biofuel such as ethanol is a replacement of gasoline which is obtained by fermentation of biomass using. Enzymes and by decomposition through bacterial action in the absence of air . The rotting of biomass in a closed tank called digester produces biogas which can be piped out to use for cooking and heating.
Question: 24
How sunlight is directly converted into electricity by solar cells?
Answer: 24
24-47
By using semiconductor devices,the solar cell also called photo voltaic cell, sunlight can be directly converted into electricity. These solar cells are made of silicon wafers. Electron in the silicon gain energy from sunlight to create a voltage. Voltage can be increased by increasing the number of solar cells.
Question: 25
How heat is generated within the Earth?
Answer: 25
25-47
Heat within the earth is generated by the following process.
  1. Radioactive decay
  2. Residual heat of the earth (usually within 10km of earth's surface).
  3. Compression of material deep inside the earth.
Question: 26
How electrical energy can be obtained from sunlight by indirect conversion method?
Answer: 26
26-47
By using semiconductor devices, the solar cell also called photo voltaic cell: sunlight can be directly converted into electricity. These solar cells are made of silicon wafers. Electron in the silicon gain energy from sunlight to create voltage.Voltage can be increased by increasing the number of solar cells.
Question: 27
Name at least two renewable and two non-renewable energy sources.
Answer: 27
27-47
The renewable source of energy are:
  1. Wind
  2. Tides
  3. Biomass
  4. Sunlight
The non-renewable sources of energy are
  1. Coal
  2. Natural gas
  3. Oil
  4. Uranium
Question: 28
Differentiate between geyser and aquifer.
Answer: 28
28-47
Geyser isa hot spring that discharges steam and hot water, intermittently releasing an explosive column into the air

Aquifer is a layer of rock holding water that allows water to percolate through it with pressure.
Question: 29
Explain briefly how the energy is obtained from the fermentation of biomass.
Answer: 29
29-47
Biofuel such as ethanol is a replacement of gasoline. It is obtained by fermentation of biomass using enzymes and by decomposition through bacterial action in the absence of air.
The rotting of biomass in a closed tank called a digester produces biogas which can be pipped out to use for cooking and heating
Question: 30
Define Kinetic energy ?
Answer: 30
30-47
Kinetic Energy (K.E):The energy in the body due to its motion is known as kinetic energy.
Question: 31
What is Salter's duck?
Answer: 31
31-47
Salter's duck is a device which can be used to utilize the water waves energy and to generate electricity .It consists of two parts
  1. Duck float
  2. Balance float
The wave energy makes duck float move relative to the balance float. The relative motion of the duck float is then used to run electricity generators.
Question: 32
Write some methods to obtain solar energy.
Answer: 32
32-47
Solar energy can be used directly to heat water using large solar reflectors (mirrors) and thermal absorbers.
Semi-conductor devices called solar cells are used to convert sunlight into electricity. Solar cells are thin wafers made from silicon,
For cloudy days or nights, electric energy can be saved in Nickel cadmium batteries by connecting them to solar panels.
Question: 33
What is solar constant ? What is its value?
Answer: 33
33-47
Solar energy at incidence outside the Earth's atmosphere is about 1.4kw m-2 which is referred as solar constant.
Question: 34
Discuss the work done in gravitational Field?
Answer: 34
34-47
Alternate Text
Question: 35
Discuss the work-energy principal ?
Answer: 35
35-47
Consider a body of mass 'm' placed on the ground. Now if some force 'F' is applied on the body, then the body will start motion with initial velocity V1in the direction of applied force. If we neglect the force of friction then the body will continue its motion
Question: 36
Write down two sources of energy which are renewable
Answer: 36
36-47
The renewable sources of energy are:
  1. Hydroelectric Energy
  2. Wind Energy
  3. Tides Energy
  4. Biomass Energy
  5. Sunlight Energy
Question: 37
Describes four uses of solar cells.
Answer: 37
37-47
Solar cells are used.
  1. To power satellites
  2. In remote ground based weather stations
  3. In rain forest communication systems
  4. In solar calculators
Question: 38
What are renewable & non-renewable energy sources? Give example of each .
Answer: 38
38-47
Renewable energy is derived from natural processes that are replenished constantly . Such as wind tides etc.
Non-renewable energy source is a source that does not renew itself. Such as coal, natural gas etc.
Question: 39
What is 'Aquifer'?`
Answer: 39
39-47
Aquifer is a layer of rock holding water that allows water to percolate through it with pressure.
Question: 40
Define and explain work ?
Answer: 40
40-47
Work:The scalar product of force and displacement is known as work.
Explanation:Consider a force 'F' is acting on a body of mass 'm' and moves it form point 'A' to point 'B' through a displacement 'd'
Work = Force * displacement
W = F*d cosO

Question: 41
Define power and instantaneous power?
Answer: 41
41-47
Power:The power of doing work is known as power. It is represented by 'P' and is given by
Power = work/time
P = w/t
Instantaneous Power:The rate of doing work in the limit when 't' approaches to zero is known as instantaneous power.
Question: 42
Define energy ? write the units of energy?
Answer: 42
42-47
Energy:The capacity of a body to do work is known as energy.
Unit of Energy:Joule, Kilo, Mega joule, kilo watt . hour are the units of energy.
Question: 43
What is conservation field ? Give example . (OR) Loop?
Answer: 43
43-47
Conservation Field:A field is said to be conservation field if the work down in it along a closed path is equal to zero.
Example:
  1. Gravitational field
  2. Electrostatic Field
  3. Magnetic field
Loop:A closed path is that path in which a body reaches to its starting point again after passing through several points.
Question: 44
How energy can be obtained from waste products?
Answer: 44
44-47
Wate products like wood waste, crop residue, and municipal solid waste is burnt in a confined container. Heat produced in this way is directly utilized in the boiler to produce steam that can run turbine generator.
Question: 45
Show that work done in a gravitational Field is independent of the path ?
Answer: 45
45-47
Alternate Text
Question: 46
Discuss the work done by a variable force ?
Answer: 46
46-47
Consider a body of mass 'm' allowed to move from point 'A' to 'B' under the action of variable force
Question: 47
What is a machine ? Discuss the input and output and efficiency of a mechanical machine ?
Answer: 47
47-47
Machine:A machine is a thing or device with the help of which we can do more work than we can do by hands.
Input of Mechanical machine:The amount of work dine on a machine by a given effort force is known as input of machine.
Input = effort *effort arm
Input = P*d
Output of Mechanical Machine:The amount of work done by a machine on the load (weight) is known as output of the machine
output = load * load arm
output = w*d
Efficiency:The ratio of output and input of a machine is known as efficiency
Efficiency:Output / input
n = w*d/ p*d

11th Class Physics Chapters Short Questions