physics last revision for 10th

1. Target ICSE Last Minute Revision: Physics
1. What is work function? A good quality cathode should have a low work function. Why?
Solution: Work function is the minimum energy (measured in electron volts) needed to remove an
electron from a solid to a point immediately outside the solid surface. Work Function is a property of the
metal. So certain metals will require more amount of energy to emit electrons while other metals will
require less.
For a metal having low work function, electron gets liberated easily by applying less energy and
hence a good quality cathode has lower work function.
2. What do you mean by secondary emission? Mention one of its uses.
Secondary emission in physics is a phenomenon where primary electrons of sufficient energy, when
hitting a surface or passing through some material, induce the emission of secondary electrons. The
number of secondary electrons emitted per incident particle is called secondary emission yield.
3. Fill in the atomic number and mass number of X1 and X2 as shown below.
Answer:
4. Why a wire mesh is used in hot cathode ray tube in front of the two vertical deflecting graphite
plates.
Ans: This mesh acts like a lens for electrons and has the effect of roughly doubling the deflection of the
electron beam, allowing the use of a larger faceplate for the same length of tube envelope
5. Why is earthing required in a household circuit?
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2. Target ICSE Last Minute Revision: Physics
Ans: Whenever there is a high voltage in the circuit, the flow of current increases in the appliance and
there is a chance of the appliance getting damaged due to the high amount of heat generated.
With earthing in place, the excess amount of current gets in the earth which is considered as zero
potential, therefore the appliance is saved as the increased current flows into the earth through the
earthing.
6. North pole of a magnet is moved away from a solenoid. What would be the polarity of the solenoid
facing the North pole? State the law used to determine the answer.
Ans: When North pole of the magnet is moved away from the solenoid, the face of the solenoid facing
the magnet becomes South Pole and it attracts the magnet.
This is described by Lenz’s law which states : When an emf is generated by a change in magnetic flux
according to Faraday's Law, the polarity of the induced emf is such that it produces a current whose
magnetic field opposes the change which produces it.
7. In an electricity distribution network, why is the voltage stepped up by a transformer?
Answer: For an electricity distribution network voltages must be stepped up before power is
transmitted great distances over power lines. Power is lost between the power plant and the
consumers because currents use some of the power to heat the transmission lines. The power
transmitted along the line is equal to the voltage times the current. The higher the voltage the lower the
current that must flow within the transmission lines to deliver the same power. Lower currents produce
much less heating and much less power loss.
8. What is the function of a slip ring in an AC dynamo?
Answer: One slip ring is connected to each end of the loop of wire to carry the current which is
generated by the rotation of that loop via the brushes to the external circuit.
9. Explain potential difference between two points.
The unit +ve charge at infinity is required to bring at pint A which is a unit positive charge. We know that
similar charges repel. Therefore we need to do some work in bringing the charge from infinity to point
A. The work done is equivalent to the energy spent in bringing the charge and is defined as the potential
at point A.
Now let us consider another point B. The work done to bring another positive charge to point B is WB.
So potential at B, VB=WB/q
The potential difference between A and B is thus
VA-VB=WA/q-WB/q
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3. Target ICSE Last Minute Revision: Physics
10. Copy the diagram below and show the direction of the deflection of the needle in the magnetic
compass.
Direction of current
Magnetic
Compass
Answer:
Direction of current
11. How is an electron volt related to energy?
Answer: Electron volt is defined as the amount of energy gained by an electron when it accelerates in an
electric field of potential difference of 1V.
So, it is the measure of kinetic energy gained by the electron.
12. What are the properties of sound wave produced by a sitar?
Answer: Properties of sound wave produced by Sitar are such that vibrations produced by Sitar are
uniform and regular.
13. Explain the principle of Sonar.
Answer: SONAR stands for Sound Navigation and Ranging. It is used to determine the depth of water
and to locate any underwater objects. It works on the principle that ultrasonic waves are triggered from
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4. Target ICSE Last Minute Revision: Physics
a SONAR device and the time between the propagation of sound and the reception of echo is measured
to calculate the distance (depth) of the bottom of the ship and the sea bed.
14. What do you mean by resonance and how can resonance be avoided while walking in a group over
the bridge.
Answer: Resonance is the tendency of a system (usually a linear system) to oscillate with larger
amplitude at some frequencies than at others. These are known as the system's resonant frequencies
(or resonance frequencies). At these frequencies, even small periodic driving forces can produce large
amplitude oscillations.
While walking in a group over a bridge, steps should not be taken simultaneously which can create
resonance.
15. What is latent heat of fusion?
Answer: Latent heat of fusion is the heat applied to ice in order to change it's state from solid to liquid.
16. State the principle of calorimetry.
Answer: Principle of calorimetry states that If two substances of different temperature are in thermal
contact and if no heat is allowed to go out or enter into and if no chemical reactions takes place in
between the two bodies then heat lost by the hotter body will be equal to the heat gained by the colder
body.
i.e.heat lost=heat gained
17. Complete the ray diagram of the path of light traveling through prism as shown below.
Answer:
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5. Target ICSE Last Minute Revision: Physics
18. Where will an image be formed in a convex lens while the image is at the focus?
Answer: In a convex lens, image will be formed at infinity.
19. By what height will a coin be raised while viewed through a glass slab of thickness‘t’?
Answer: The coin will be raised by a height of t(1-1/n), where n is the refractive index.
Let ‘t’ be the thickness of the glass slab.
Let ‘t1’ be the apparent height of the coin through the glass slab.,
We know that , n=Real Depth/ Apparent depth,
So, n=t/t1, or t1=t/n
The coin will be raised by a distance= Real Depth- apparent Depth
= t-t/n
= t(1-1/n)
20. Explain the working of an optical fiber with the help of a ray diagram.
Answer: Fiber optics are used to transmit light signals over long distance. They work on the principle of
total internal reflection.
21. Why are wine bottles kept under water in cold countries?
Answer: Water has high specific heat capacity. Therefore, it takes longer time for water to become ice
and therefore the wine bottles stored under water do not freeze.
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6. Target ICSE Last Minute Revision: Physics
22. Why is water used as a coolant in car radiator?
Answer: Water is used as coolant car radiators because of its high specific heat capacity. Water can
absorb a large amount of heat energy from the engine of the car, but its temperature does not rise too
high.
23. Using graph, show the relationship between angle of incidence and the angle of deviation for a
prism.
Answer:
24. What is the transformation of energy that is taking place in a )AC dynamo b) DC Motor.
a) AC Dynamo: Mechanical energy is transformed to electrical energy.
b) DC Motors: Electrical energy is transformed to mechanical energy.
25. Differentiate between renewable and non-renewable energy.
Answer:
Nonrenewable Renewable
1. The non-renewable sources of energy that 1. The sources of renewable energy is abundant
we are using are limited and are bound to in nature.
expire one day.
2. Non-renewable sources release toxic gases 2. They have low carbon emission and
(e.g.carbon-di-oxide, nitric oxide etc) in the air therefore considered as environmental friendly.
when burnt which are the major cause for
global warming.
3. These are quite cheap, easy to use. 3. These are quite costly.
26. Why is class 3 lever used?
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7. Target ICSE Last Minute Revision: Physics
Answer: Class 3 levers do no multiply force but they are used to change the direction of the applied
force.
27. Prove that the MA of an inclined plane is always greater than one.
Answer:In case of an inclined plane, Mechanical Advantage of the plane is given by,
MA= Slant height/ Vertical height.
Since slant height is always greater than the vertical height, MA > 1.
28. What is the relationship between MA, VR and efficiency? Which one of these quantities is constant
for a machine?
Answer: Efficiency=MA/VR
Efficiency is constant.
29. What are the forces acting in a moving rocket?
Answer: Forces acting on a moving rocket are:
Drag, weight, thrust, resistance.
30. State the principle of moments and explain how it is used in simple machines.
Answer: Principle of moment states that if a body is in equilibrium under the action of a number of
forces, then the algebraic sum of the moments of the forces about any point is equal to zero.
Simple machines like lever works on the principle of moments. Levers have a fulcrum and has load and
effort applied at different points.
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