# Physics - Electromagnetic Spectrum

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Quizzes Created: 1 | Total Attempts: 796
Questions: 20 | Attempts: 796

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• 1.

### A group of wavelengths (or) frequencies is known as

• A.

Group of colours

• B.

Spectrum

• C.

Colour band

• D.

None

B. Spectrum
Explanation
A group of wavelengths or frequencies is known as a spectrum. This term is commonly used in physics and refers to the range of colors or electromagnetic radiation that is produced when white light is passed through a prism or diffracted. The spectrum includes all the different wavelengths or frequencies of light, from red to violet, and can be seen as a continuous band of colors.

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• 2.

• A.

Mechanical

• B.

Longitudinal

• C.

Transverse

• D.

Stationary

C. Transverse
Explanation
Electromagnetic radiation waves are transverse. This means that the oscillations of the waves occur perpendicular to the direction of wave propagation. Unlike mechanical waves, such as sound waves, electromagnetic waves do not require a medium to travel through. They can travel through a vacuum, as well as through different mediums like air or water. Transverse waves are characterized by their ability to exhibit properties like reflection, refraction, and interference. These properties are observed in electromagnetic waves, which include various types such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

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• 3.

### Electric heater emits

• A.

• B.

Visible spectrum

• C.

UV rays

• D.

Micro waves

Explanation
An electric heater emits infrared (IR) radiations. IR radiations are a form of electromagnetic radiation that is not visible to the human eye. When an electric heater is turned on, it produces heat by converting electrical energy into thermal energy. This thermal energy is then emitted as IR radiations, which can be felt as heat by our skin. Unlike visible light, which is part of the visible spectrum, IR radiations have longer wavelengths and lower frequencies.

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• 4.

### A device that can't absorb IR-radiations is

• A.

Flint glass

• B.

Borosilicate glass

• C.

Hard glass

• D.

Soda glass

D. Soda glass
Explanation
Soda glass is a type of glass that cannot absorb IR-radiations. This is because soda glass is made from a mixture of silica, soda ash, and limestone, which have a low absorption coefficient for infrared radiation. On the other hand, flint glass, borosilicate glass, and hard glass are all capable of absorbing IR-radiations to some extent due to their different compositions and properties.

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• 5.

### Prisms made up of the following is used to observe the infrared radiations

• A.

Ordinary glass

• B.

Rock salt

• C.

Epsom Salt

• D.

None

B. Rock salt
Explanation
Rock salt is used to make prisms for observing infrared radiation because it has a high transmittance in the infrared region of the electromagnetic spectrum. Ordinary glass and Epsom salt do not have the same level of transmittance in the infrared range, making them unsuitable for observing infrared radiation. Therefore, rock salt is the most appropriate material for making prisms that can effectively observe infrared radiations.

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• 6.

### Which of the following emits infrared radiations ?

• A.

Hot iron

• B.

Ice

• C.

Freezing mixture

• D.

Wet cloth

A. Hot iron
Explanation
Hot iron emits infrared radiations because it has a high temperature. Infrared radiation is a form of electromagnetic radiation that is emitted by objects with a temperature above absolute zero. As the iron gets heated, the atoms and molecules in it vibrate faster, and this vibration produces infrared radiation. This radiation is not visible to the human eye but can be felt as heat. Therefore, hot iron is the correct answer as it emits infrared radiations.

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• 7.

### The velocity of electromagnetic waves C=

• A.

ν/λ

• B.

νλ

• C.

λ/ν

• D.

ν+λ

B. νλ
Explanation
The correct answer is νλ. This is because the velocity of electromagnetic waves (C) is equal to the product of the frequency (ν) and the wavelength (λ).

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• 8.

### The direction of propagation of electro magnetic waves

• A.

Perpendicular to only electric field

• B.

Perpendicular to only magnetic field

• C.

Electric and magnetic fields perpendicular to each other and also perpendicular to the direction of their propagation

• D.

None

C. Electric and magnetic fields perpendicular to each other and also perpendicular to the direction of their propagation
Explanation
Electromagnetic waves consist of both electric and magnetic fields that oscillate perpendicular to each other. These fields are also perpendicular to the direction in which the wave is propagating. This is known as transverse wave motion. Therefore, the correct answer is that the electric and magnetic fields are perpendicular to each other and also perpendicular to the direction of their propagation.

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• 9.

### The wavelength limit of visible spectrum

• A.

0.1 µm - 0.7 µm

• B.

0.4 µm - 0.7 µm

• C.

0.7 µm - 1.0 µm

• D.

0.2 µm - 0.9 µm

B. 0.4 µm - 0.7 µm
Explanation
The correct answer is 0.4 µm - 0.7 µm. This range represents the wavelengths of light that can be detected by the human eye. Light with a wavelength shorter than 0.4 µm is in the ultraviolet range, which is not visible to humans. Light with a wavelength longer than 0.7 µm is in the infrared range, which is also not visible to humans. Therefore, the visible spectrum is limited to wavelengths between 0.4 µm and 0.7 µm.

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• 10.

### Visible spectrum is due to :

• A.

Excitation of ē s

• B.

Deexcitation of ē s

• C.

Vibrated atoms

• D.

Rotation of atoms

A. Excitation of ē s
Explanation
The visible spectrum is due to the excitation of electrons. When electrons absorb energy, they move to higher energy levels, and when they release energy, they move back to lower energy levels. This process of excitation and deexcitation of electrons is responsible for the emission and absorption of light in the visible range. Vibrated atoms and rotation of atoms do not directly contribute to the visible spectrum.

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• 11.

### The charateristic colour emitted by the substance is depends on

• A.

The colour of the substance

• B.

The state of the substance

• C.

Characteristic properties of the atoms present in the substance

• D.

None

C. Characteristic properties of the atoms present in the substance
Explanation
The characteristic color emitted by a substance depends on the characteristic properties of the atoms present in the substance. Different atoms have different energy levels and electron configurations, which determine the wavelengths of light that they can absorb and emit. When atoms in a substance absorb energy, they move to higher energy levels, and when they release energy, they move back to lower energy levels, emitting specific wavelengths of light in the process. Therefore, the characteristic properties of the atoms in a substance determine the color of light that it emits.

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• 12.

### The wavelength limit of IR is .....

• A.

0.1 µm - 0.7 µm

• B.

0.7 µm - 100 µm

• C.

10 µm - 10 m

• D.

1 m - 100 km

B. 0.7 µm - 100 µm
Explanation
The correct answer is 0.7 µm - 100 µm. Infrared (IR) radiation refers to electromagnetic waves with longer wavelengths than visible light. The wavelength range of 0.7 µm - 100 µm corresponds to the infrared region of the electromagnetic spectrum. This range is commonly used in applications such as thermal imaging, remote sensing, and communication.

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• 13.

### Which of the following is used to detect the IR ?

• A.

Thermometers

• B.

Thermopiles

• C.

Bolometer

• D.

All

D. All
Explanation
All of the options listed (thermometers, thermopiles, and bolometers) can be used to detect infrared (IR) radiation. Thermometers can measure temperature by detecting the heat emitted by an object, which includes IR radiation. Thermopiles are specifically designed to detect IR radiation and convert it into an electrical signal. Bolometers are highly sensitive detectors that can measure even small amounts of IR radiation. Therefore, all of these options can be used to detect IR radiation.

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• 14.

### The rays emitted by molecules when they change their state of rotational or vibrational motion are

• A.

Visible spectrum

• B.

Micro waves

• C.

• D.

Infrared waves

D. Infrared waves
Explanation
When molecules change their state of rotational or vibrational motion, they emit rays in the form of electromagnetic radiation. These rays have longer wavelengths and lower frequencies than visible light, which places them in the infrared region of the electromagnetic spectrum. Therefore, the correct answer is "Infrared waves."

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• 15.

### The radiations, those find application in physio - therapy are

• A.

Visible spectrum

• B.

Micro waves

• C.

Infrared waves

• D.

C. Infrared waves
Explanation
Infrared waves are used in physiotherapy because they have the ability to penetrate deep into the body, promoting healing and providing pain relief. These waves generate heat in the tissues, increasing blood circulation and relaxing muscles. This makes them effective in treating conditions such as muscle strains, arthritis, and joint stiffness. Unlike visible spectrum, microwaves, and radio waves, infrared waves have specific therapeutic properties that make them suitable for physiotherapy applications.

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• 16.

### The wavelength range of microwaves is

• A.

0.1 µm - 0.7 µm

• B.

10 µm - 10 m

• C.

0.7 µm - 100 µm

• D.

0.4 µm - 1 nm

B. 10 µm - 10 m
Explanation
Microwaves are a type of electromagnetic radiation with longer wavelengths than visible light. The wavelength range of microwaves is typically between 10 µm and 10 m. This range allows microwaves to be used for various applications, such as cooking, communication, and radar systems.

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• 17.

### Micro waves are produced when

• A.

Excited electrons in atoms jump back to their normal states

• B.

Electromagnetic oscillators oscillate with high frequency

• C.

Electrons are accelerated

• D.

Transitions of the electrons in atoms

B. Electromagnetic oscillators oscillate with high frequency
Explanation
Micro waves are produced when electromagnetic oscillators oscillate with high frequency. This is because microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter. These waves are generated by devices called electromagnetic oscillators, which produce oscillations of electric and magnetic fields at a high frequency. As the oscillators oscillate rapidly, they create microwaves that can be used for various purposes such as cooking, communication, and radar systems.

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• 18.

### Micro waves are used in

• A.

• B.

Telemetry

• C.

Micro wave oven

• D.

All the above

D. All the above
Explanation
Microwaves are used in radar systems to detect and track objects, as well as in telemetry systems to transmit data wirelessly. Additionally, microwaves are utilized in microwave ovens to cook food by generating heat through the absorption of microwave energy by water molecules in the food. Therefore, the correct answer is "all the above" as microwaves are used in radar, telemetry, and microwave ovens.

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• 19.

### Radio waves are produced when

• A.

Electromagnetic oscillators oscillate with low frequency

• B.

Electromagnetic oscillators oscillate with high frequency

• C.

Transition of electrons in atoms

• D.

Excited electrons in atoms jump back to their normal state

A. Electromagnetic oscillators oscillate with low frequency
Explanation
Radio waves are a type of electromagnetic wave, and they are produced when electromagnetic oscillators oscillate with low frequency. This oscillation generates the changing electric and magnetic fields that make up the radio wave. Higher frequency oscillations would produce waves with shorter wavelengths, such as microwaves or visible light. The transition of electrons in atoms or the excited electrons in atoms jumping back to their normal state do not directly produce radio waves.

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• 20.

### Mapping of the radio emissions from extra-terrestrial sources is termed as

• A.

Halography

• B.

• C.

Meteorology

• D.

None