Question Bank for 12th Class Physics EM Waves Case Based (MCQs) - Electromagnetic Waves

The spectrum of electromagnetic radiation contains a part known as microwaves. These waves have frequency and energy smaller than visible light and wavelength larger than it. What is the principle of a microwave oven and how does It work? Our objective is to cook food or warm it up. All food items such as fruit, vegetables, meat, cereals, etc., contain water as a constituent. Now, what does it mean when we say that a certain object has become warmer? When the temperature of a body rises, the energy of the random motion of atoms and molecules increases and the molecules travel or vibrate or rotate with higher energies. The frequency of rotation of water molecules is about 2.45 gigahertz (GHz). If water receives microwaves of this frequency, its molecules absorb this radiation, which is equivalent to heating up water. These molecules share this energy with neighbouring food molecules, heating up the food. One should use porcelain vessels and non-metal containers in a microwave oven because of the danger of getting a shock from accumulated electric charges. Metals may also melt from heating. The porcelain container remains unaffected and cool, because its large molecules vibrate and rotate with much smaller frequencies, and thus cannot absorb microwaves. Hence, they do not get eaten up. Thus, the basic principle of a microwave oven is to generate microwave radiation of appropriate frequency in the working space of the oven where we keep food. This way energy is not wasted in heating up the vessel. In the conventional heating method, the vessel on the burner gets heated first and then the food inside gets heated because of transfer of energy from the vessel. In the microwave oven, on the other hand, energy is directly delivered to water molecules which is shared by the entire food.

As compared to visible light microwave has frequency and energy:

A)

more than visible light.

B)

less than visible light.

C)

equal to visible light.

D)

Frequency is less but energy is more

View Solution

2)

When the temperature of a body rises:

A)

the energy of the random motion of atoms and molecules increases.

B)

the energy of the random motion of atoms and molecules decreases.

C)

the energy of the random motion of atoms and molecules remains same.

D)

the random motion of atoms and molecules becomes streamlined.

View Solution

3)

The frequency of rotation of water molecules is about:

A)

2.45 MHz.

B)

2.45 kHz.

C)

2.45 GHz.

D)

2.45 THz.

View Solution

4)

Why should one use porcelain vessels and non- metal containers in a microwave oven?

A)

Because it will get too much hot.

B)

Because it may crack due to high frequency.

C)

Because it will prevent the food items to become hot.

D)

Because of the danger of getting a shock from accumulated electric charges.

View Solution

5)

In the microwave oven,

A)

energy is directly delivered to water molecules which is shared by the entire food.

B)

the vessel gets heated first, and then the food grains inside.

C)

the vessel gets heated first and then the water molecules collect heat from the body of the vessel.

D)

energy is directly delivered to the food grains.

View Solution

6)

Directions (Q. No. 6 to 10):

Read the following text and answer the following questions on the basis of the same:

Laser:

Electromagnetic radiation is a natural phenomenon found in almost all areas of daily life, from radio waves to sunlight to x-rays. Laser radiation - like all light - is also a form of electromagnetic radiation. Electromagnetic radiation that has a wavelength between 380 nm and 780 nm is visible to the human eye and is commonly referred to as light. At wavelengths longer than 780 nm, optical radiation is termed infrared (IR) and is invisible to the eye. At wavelengths shorter than 380 nm, optical radiation is termed ultraviolet (UV) and is also invisible to the eye. The term "laser light" refers to a much broader range of the electromagnetic spectrum that just the visible spectrum, anything between 150 nm up to 11000 nm (i.e. from the UV up to the far IR). The term laser is an acronym which stands for "light amplification by stimulated emission of radiation".

Einstein explained the stimulated emission. In an atom, electron may move to higher energy level by absorbing a photon. When the electron comes back to the lower energy level it releases the same photon. This is called spontaneous emission.

This may also so happen that the excited electron absorbs another photon, releases two photons and returns to the lower energy state. This is known as stimulated emission.

Laser emission is therefore a light emission whose energy is used, in lithotripsy, for targeting and ablating the stone inside human body organ.

Apart from medical usage, laser is used for optical disk drive, printer, barcode reader etc.

What is the full form of LASER?

A)

Light amplified by stimulated emission of radiation

B)

Light amplification by stimulated emission of radiation

C)

Light amplification by simultaneous emission of radiation

D)

Light amplified by synchronous emission of radiation

View Solution

7)

The "stimulated emission" is the process of :

A)

release of a photon when electron comes back from higher to lower energy level.

B)

release of two photons by absorbing one photon when electron comes back from higher to lower energy level.

C)

absorption of a photon when electron moves from lower to higher energy level.

D)

None of the above

View Solution

8)

What is the range of amplitude of LASER?

A)

150 nm - 400 nm

B)

700 nm -11000 nm

C)

Both the above

D)

None of the above

View Solution

9)

Lithotripsy is:

A)

an industrial application.

B)

a medical application.

C)

laboratory application.

D)

process control application.

View Solution

10)

LASER is used in:

A)

optical disk drive.

B)

transmitting satellite signal.

C)

radio communication.

D)

ionization.

View Solution

11)

Directions (Q. No. 11 to 15):

Read the following text and answer the following questions on the basis of the same:

Ozone layer depletion:

We are all exposed to UV radiation from the sun.

The sun is by far the strongest source of ultraviolet radiation. UV radiation spectrum is divided into three regions called UVA, UVB and UVC. As sunlight passes through the atmosphere, all UVC and most UVB is absorbed by ozone, water vapour, oxygen and carbon dioxide. UVA is not filtered as significantly by the atmosphere.

The three types of UV radiation are classified according to their wavelength. They differ in their biological activity and the extent to which they can penetrate the skin. The shorter the wavelength, the more harmful the UV radiation.

The UV region covers the wavelength range 100-400 nm and is divided into three bands:

UVA (315-400 nm)

UVB (280-315 nm)

UVC (100-280 nm).

Short-wavelength UVC is the most damaging type of UV radiation. However, it is completely filtered by the atmosphere and does not reach the earth's surface.

UV level reaching the earth changes with latitude and altitude.

UV levels are higher closer to the equator, Closer to the equator the sun's rays have a shorter distance to travel through the atmosphere and therefore harmful UV radiation absorption is less.

With increasing altitude less atmosphere is available to absorb UV radiation. With every 1000 m in altitude, UV levels increase by approximately 10% Ozone is a particularly effective absorber of UV radiation. As the ozone layer gets thinner, the protective filter activity is progressively reduced.

Consequently, the people and the environment are exposed to higher levels of UV radiation, especially UVB.

Ozone depletion is caused by human-made chemicals released into the atmosphere.

How many bands are there in UV radiation spectrum?

A)

2

B)

5

C)

3

D)

4

View Solution

12)

Most harmful UV radiation band is

A)

UVA

B)

UVB

C)

UVC

D)

all of them

View Solution

13)

Which UV band is not absorbed by the atmosphere?

A)

UVA

B)

UVB

C)

UVC

D)

none of them

View Solution

14)

Ozone layer depletion is caused by

A)

cosmic rays.

B)

human-made chemicals released into the atmosphere.

C)

electrical spark in the atmosphere.

D)

None of the above

View Solution

15)

UV level is

A)

low at equator, high at poles.

B)

low at poles, high at equator.

C)

same at pole and equator.

D)

None of the above

View Solution

12th Class Physics EM Waves Question Bank

done Case Based (MCQs) - Electromagnetic Waves Total Questions - 15

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Case Based (MCQs) - Electromagnetic Waves

Case Based (MCQs) - Electromagnetic Waves Total Questions - 15