Students should refer to Modern Physics ICSE Class 10 Physics Board Exam Questions provided below with solutions. These will help the students to understand the type of questions which have been asked in previous year examinations and the type of solutions which the student should give to get good marks. You should also refer to ICSE Class 10 Physics Sample papers for more practice
ICSE Class 10 Physics Modern Physics Important Questions
Students should learn the important questions and answers given below for Chapter Modern Physics in Physics for ICSE Class 10. These board questions are expected to come in the upcoming exams. Students of ICSE Class 10th should go through the Important questions and answers ICSE Class 10 Physics which will help them to get more marks in exams.
Modern Physics ICSE Class 10 Physics Board Exam Questions
Modern Physics ICSE Class 10 Physics Board Exam Questions
1) Can we use aluminium or steel as a target in X-ray production experiment? If not give a reason?
Target should be of a material of high atomic weight and high melting point. If the metal is of high melting point, it will not melt due to heat developed due to the collision of electrons. High atomic weight metal will emit X-rays of high energy. T his limits the choice of anode material to chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), molybdenum (Mo), and a
few other less commonly used materials for X-ray powder diffraction.
2) Why do doctors wear lead aprons and spectacles while working near X-ray machine?
Any test that involves x-rays or radioactive isotopes exposes the people nearby to potentially harmful radiation. This is especially true for doctors, nurses and technicians who work around radiation day in and day out. X-rays do not penetrate the lead and thus doctor’s body is not exposed to X-rays.
3) How are β-rays emitted from a nucleus while it does not contain electrons?
β-rays are emitted from the nucleus due to conversion of a neutron into a proton, an electron and antineutrino. This electron is emitted from the nucleus in the form of β-rays.
4) A radioactive substance is oxidised. What change would you expect to take place in the nature of its radioactivity? Give a reason for your answer.
There will be no change in the nature of its radioactivity because radioactivity is a nuclear phenomenon and oxidation does not affect the nucleus of the substance.
5) A mass of lead is embedded in a block of aluminium (2 mm thick). Radiations from a radioactive source incident on the side of the block produce a shadow on a fluorescent screen placed beyond the block. The shadow of the block of aluminium is fainter than the shadow of lead. Give the reason for this difference.
The shadow of the block of aluminium is fainter than the shadow of the lead because the α-radiations (least penetrating power) are stopped by aluminium block while β and γ radiations due to high penetrating power pass through it while lead block does not allow α, β and γ radiations to pass through it.
6) ‘Radioactive materials as an alternative source of energy must be used wisely’. Give reasons to justify this statement.
Radioactive materials as an alternative source of energy must be used wisely because these materials emit harmful radiations. The emission of harmful radiations cannot be controlled because the activity of radioactive materials is unaffected by any chemical or physical change i.e., heating, freezing, applying strong electric or magnetic field or change of temperature or pressure.
It is true that nuclear power plants are major sources of energy but a large amount of radioactive materials and radiations escape to the atmosphere.
These materials can cause nausea, vomiting, fever, diarrhoea, loss of hair, leukaemia, cancer, genetic effects and ultimately death. Waste materials are pollutants which create land and soil pollution. When radiations of these materials enter the human body they kill the living tissues and cause radiation burns and genetic effects. This is why these materials are kept in thick lead blocks/containers with a very narrow opening so as to stop radiations coming out from other directions.
7) A radioactive substance is oxidised. What change would you expect to take place in the nature of its radioactivity? Give a suitable reason.
If a radioactive substance is oxidised, no change takes place in the nature of its radioactivity. If the phenomenon of radioactivity is due to orbital electrons it would have been affected but it is the property of nucleus. That is why the nature of radioactivity of the oxidised substance is unaffected.
Miscellaneous Questions and Answers
1) The wires leading the current to an electric bulb are thick while the wire inside the bulb is very fine. Give reason?
Filament of the bulb and supply wires are connected in series so the same current flows in the connecting wires and the bulb. Now we know that thick wires have less resistance and very fine wires will have a large resistance. Here we also know that heat produced due to given current is directly proportional to the resistance (H ∞ R). Therefore,
due to less/negligible resistance of the thick supply wires, the connecting wires remain practically unheated while due to the very large resistance of fine filament, a large amount of heat is produced in the filament, hence the bulb glows.
2) In a coil carrying current, how will you determine the polarity by seeing the direction of current? Explain?
Look at the face of the coil, if the current around that face is in an anticlockwise direction, the face has north polarity, while if the current at the face is in the clockwise direction, the face has south polarity. This can be tested by using a compass needle.
3) Why is it advisable to view a TV screen from a distance of about 12 feet?
In a TV set electrons are accelerated by about 5000V and strike the screen due to which soft X-rays are produced which can damage our body. These X-rays are absorbed by a length of few feet of air due to ionization by collisions. Thus, it is advisable to watch TV from a distance of nearly 10-12 feet.
4) Why hydrogen is considered very efficient cooling gas for enclosed electric generators?
Due to the high specific heat capacity of hydrogen coupled with its high thermal conductivity, it is a very efficient cooling gas for enclosed electric generators.
5) Why is steam used for running trains?
Due to the high specific latent heat of steam, it releases very large amount of heat energy during condensation which gets converted into mechanical energy of the train
6) Why is it more economical to transmit electrical energy at high voltage and low current?
The loss of energy along the transmission lines is proportional to the square of current (H ∞ i 2 ). Hence, the transmission of electrical energy is economical at high voltage
and low current.
7) Why is the longer handle of a water pump preferred? Explain.
Longer the effort arm of the handle of the water pump, lesser is the effort required to operate the pump because the increase in the effort arm increases the mechanical advantage.
8) Why does the thoriated tungsten (tungsten coated with carbon and thorium) preferred as an electron emitter over tungsten?
Thoriated tungsten is preferred as an electron emitter over tungsten because thoriated tungsten work function is 2.6eV while pure tungsten work function is 4.52eV.
Thoriated tungsten needs to be heated to only 2000K to emit electrons while tungsten is to be heated to nearly 2500K.
9) You’re in a row boat, which is in a large tank filled with water. You have an anchor on board, which you throw overboard (the chain is long enough so the anchor rests completely on the bottom of the tank). Does the water level in the tank rise or fall?
It will fall. An anchor, by definition, is denser than water. Therefore, its displacement as mass (when its on the boat) is greater than its displacement as volume (when it’s in water). Therefore, if you throw it overboard, the water level falls.
10) Why will an echo not be heard when the distance between the source of the sound and the reflecting surface is 10 m?
Echo will not be heard because minimum distance between the source and the reflecting surface should be 17 m.
11) How can a person, standing in the middle of a perfectly smooth island of ice, get to a
He must throw any object on this person, in a direction opposite to his intended direction of motion. The reaction force, corresponding to this action, will then make him glide along the perfectly smooth ice surface and thus take him to the desired corner.
12) How are we able to get a sufficiently loud sound in a bell? Give reason?
Answer: Bells generally have a metal bob which is made to strike a large outer case or gong. On striking, the bob sets this gong into vibrations. This, in turn, sets a large volume of air into vibration and this results in the production of a sufficiently loud sound.
13) Why is less effort needed to lift a load over an inclined plane as compared to lifting the load directly?
An inclined plane makes work easier by reducing the exertion needed for the job while increasing the distance over which that exertion is maintained. The angle at which a load is lifted determines the amount of exertion needed to lift it. Less effort is required to lift over an inclined plane because for a given height ‘h’ longer is the length ‘l’ of the inclined plane and smaller is the angle of inclination greater is the mechanical advantage, so less will be the effort required as we know M.A. = l/h.
14) How will you investigate the existence of the radiation beyond the red and violet extremes of the spectrum?
If a blackened bulb thermometer is moved from the violet end towards the red end, first a steady rise in temperature is observed, but as the thermometer goes beyond the red end, there is a rapid rise in temperature. This shows the existence of some kind of radiation producing the heating effect beyond the red of the spectrum.
If the radiations from the red end to the violet end are made to fall on the silver chloride solution. It almost remains unaffected beyond the violet end of the spectrum.
15) Why is single movable pulley system considered superior to single fixed pulley system?
Single movable pulley system is considered superior to single fixed pulley system because its mechanical advantage is greater than single fixed pulley and hence more load can be lifted by applying comparatively less effort.
16) Explain, how the human body maintains a constant temperature of about 98.4 0F even when the outside temperature may go as high as 110 ?
When the outside temperature is higher than that of our body, we sweat a lot. As the ‘sweat’ evaporates, it withdraws its latent heat of vaporisation from our body which, therefore, cools down. Thus, by sweating a lot and letting this sweat evaporate, our body is able to stay at a constant temperature of about 98.4 0 F even when the outside temperature
may be as high as 110 0 F.
17) Why does a stone lying in the sun gets heated up very much, whereas water lies in the sun for the same duration gets heated very little?
Water has the specific heat capacity equal to 4200 J/kg, which is about 5 times the specific heat capacity of the stone. So when the sun shines, water heats up very slowly whereas the stone heats up very fast. This is why the stone gets heated up very much as compared to the water.
18) Why is a voltmeter connected in parallel across a conductor in a circuit? If by mistake a voltmeter is connected in series in a circuit, what will happen?
A voltmeter is connected in parallel across a conductor in a circuit so as to measure the potential difference across the ends of the conductor.
If by mistake, a voltmeter is connected in series, due to its high resistance, negligible current will pass through it and so there will be no deflection of its pointer.
19) Is there any relationship between sunlight and fusion? If so, Give reason?
Yes, in sun and stars, fusion produced by thermonuclear reactions is the main source of energy.
20) Explain, why bottled soft drinks are more effectively cooled by cubes of ice than by iced water?
Ice needs an amount of heat equal to its latent heat of fusion (i.e., 336 10 3 J/kg), to melt and form (ice-cold) water at 0 0 C. Hence each kg of ice is able to withdraw 336 10 3 J more heat (from a given ‘hot’ drink) than ice-cold water at 0 0 C. Lumps of ice, therefore, produce more effective cooling than ice-cold water at 0 0 C.
21) How do frequency and amplitude affect a musical sound?
In musical sound, if the frequency changes the pitch of the sound changes. With the increase in the frequency of sound the pitch increases and vice versa.
And if the amplitude changes, the loudness and so the intensity of sound changes. With the increase in the amplitude the loudness increases and vice versa.
22) How would you show the presence of ultra-violet and infrared rays in the spectrum?
If a sensitive thermometer was moved along a spectrum, the thermometer showed a temperature rise even when it was moved in the spectrum. It was concluded that (invisible) heat radiations present even beyond the red end of the spectrum and named as infrared radiations. In the presence of ultra-violet radiations, the silver chloride solution becomes dark brown or black.
23) Why are burns caused by steam more severe than those caused by boiling water at the same temperature?
Steam will produce more severe burns than boiling water because steam has more heat energy than water due to its latent heat of vaporisation. When water goes from gas to liquid it is undergoing what is called a phase change. Phase changes require a lot more energy than just a temperature change.
The energy required for water to go from a liquid to a gas is called the heat of vaporization. When steam (water in the gas phase) hits your skin, a lot of energy will be released as it condenses into a liquid, undergoing a phase change.
This energy release causes a much worse burn than if the same amount of boiling water were to hit your skin where it would decrease in temperature (to your skin’s temperature) but would not have to go through a phase change. T
The loss of energy that is released from steam hitting your skin occurs quickly and in a small localized area, therefore causing damage to your cells. Besides this, steam being in the gaseous state goes deeper through the pores of skin thus causing more deep burns.
24) Why weather gets pleasant when freezing starts in cold countries?
Everyone gram of water on freezing releases 336J of heat. Thus during freezing, very large amount of heat energy is released in the atmosphere. It is this released energy which makes the weather pleasant.
25) Explain, why surroundings become pleasantly warm when water in a lake starts freezing in cold countries.
In cold countries, surroundings become pleasant when water in lakes starts freezing, because for every kilogram of water, on freezing, 336000 joules of heat energy is liberated. This heat energy, when dissipated in the atmosphere makes the weather moderate and pleasant and also slows down the process of freezing.
26) If, in a central heating system, steam enters a radiator pipe at 100 0 C and water leaves the radiator pipe at 100 , can this radiator pipe heat a room? Give reason.
In cold countries, in a central heating system, the steam of 100 0 C enters a radiator pipe at 100 0 C and water leaves the radiator pipe at 100 0 C, room is still heated, though the
temperature of entering steam and outgoing water is the same i.e., 100 0 C. the main reason is the high specific latent heat of vaporisation which is liberated when steam condenses into the water at the same temperature and this heat (2268 × 10 3 J/kg), hence dissipated in the air of the room, keeps it warm.
27) Explain the motion of a planet around the sun in a circular path.
A planet moves around the sun in a circular path for which the force of attraction on the planet by the sun provides the necessary centripetal force. Planet wants to go in a straight line unless a force is applied to it. The Sun applies gravitational force but stays in one place, so planets move and finds force coming from a new direction and keeps turning in its path due to changed direction.
28) How is sound wave produced in strings fixed at both ends?
When a string stretched between two fixed points is bowed, struck or plucked, transverse vibrations travel along the string, these are reflected at the fixed ends and a standing wave pattern is formed. The vibrations of the string give rise to longitudinal waves in the air which are transmitted to our ear.
29) Explain, why no tracks are left on the ice during ice skating.
The weight of the body acts on a very small area of skate, in comparison to that of ice. Under this high pressure, ice melts to form water below 0 0 C. The water so formed makes the surface water skating more slippery. But as soon as the skater moves further, the water does not experience any pressure and re-freezes into ice leaving no track on the ice surface.