Electromagnetic Waves

Electromagnetic waves are the waves which carry energy by the variations of electric and magnetic fields. Infrared radiation, visible light, and ultraviolet radiation are examples of Electromagnetic waves. This note provides information about electromagnetic waves.

Summary

Things to Remember

Electromagnetic waves are the waves which carry energy by the variations of electric and magnetic fields.
Visible light is defined as the form electromagnetic radiation or wavelength that are visible to human eye.
. The wavelength of infrared radiation ranges from 10^-5m to 5 \(\times\) 10^-3m.
Ultraviolet radiation is a form of electromagnetic radiation with wavelength ranging from 5 \(\times\) 10^-9m to 5 \(\times\) 10^-7m.
The wavelength of X-rays andγ- rays ranges below 5 \(\times\) 10^-8m.
X- rays are produced by electrons. X- rays are used in hospitals for medical purpose. Gamma rays are used in medical field to cure cancer.

MCQs

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Subjective Questions

Q1:

A. Write the words, from the above passage which are opposite in meaning to the following words:

(a) physically

Type: Very_short Difficulty: Easy

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Q2:

A. Write the words, from the above passage which are opposite in meaning to the following words:

(b) fine handwriting

Type: Very_short Difficulty: Easy

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Q3:

A. Write the words, from the above passage which are opposite in meaning to the following words:

Type: Very_short Difficulty: Easy

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Q4:

A. Write the words, from the above passage which are opposite in meaning to the following words:

(d) leave

Type: Very_short Difficulty: Easy

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Q5:

A. Write the words, from the above passage which are opposite in meaning to the following words:

(e) never

Type: Very_short Difficulty: Easy

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Q6:

A. Write the words, from the above passage which are opposite in meaning to the following words:

(f) difficult

Type: Very_short Difficulty: Easy

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Q7:

B. Write "T" for true and "F" for false statement:

(a) The writer is mentally healthy.

Type: Very_short Difficulty: Easy

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Q8:

B. Write "T" for true and "F" for false statement:

(b) Nima knew the rules of the games but she didn't follow them.

Type: Very_short Difficulty: Easy

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Q9:

B. Write "T" for the true and "F" the false statements:

Type: Very_short Difficulty: Easy

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Q10:

B. Write "T" for the true and "F" the false statements:

(d) Nima is looked after by her mother.

Type: Very_short Difficulty: Easy

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Q11:

B. Write "T" for the true and "F" the false statements:

(e) Nima is illiterate.

Type: Very_short Difficulty: Easy

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Q12:

B. Write "T" for the true and "F" the false statements:

(f) The writers father works in a factory.

Type: Very_short Difficulty: Easy

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Q13:

B. Write "T" for the true and "F" the false statements:

(g) Nima is mentally retarded.

Type: Very_short Difficulty: Easy

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Q14:

B. Write "T" for the true and "F" the false statements:

(h) Nima breaks a rule of game.

Type: Very_short Difficulty: Easy

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Q15:

B. Write "T" for the true and "F" the false statements:

(i) The writer's mother is a housewife.

Type: Very_short Difficulty: Easy

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Q16:

C. Rewrite the following sentences putting them in the correct order:

(a) She was then excluded from the games.

(b) Nima played games with her sister.

(d) She broke the rules.

Type: Very_short Difficulty: Easy

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Q17:

D. Answer the following questions:

(a) Why did other children laugh at her?

Type: Short Difficulty: Easy

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Q18:

D. Answer the following questions:

(b) What was the main cause of nima's abnormal behavior?

Type: Short Difficulty: Easy

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Q19:

D. Answer the following questions:

Type: Short Difficulty: Easy

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Q20:

D. Answer the following questions:

(d) Why did't the writer want Nima to join their games?

Type: Short Difficulty: Easy

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Q21:

D. Answer the following questions:

(e) What do you think of the writers's feeling towards Nima?

Type: Very_short Difficulty: Easy

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Electromagnetic Waves

Electromagnetic waves

Visible light

Visible light is defined as the form electromagnetic radiation or wavelength that are visible to human eye. Visible lights are produced by flames and discharge tubes. Wavelength of visible light ranges from 4\(\times\) 10^-7m to 8 \(\times\) 10^-7m. Long wavelength visible light is red light with 8 \(\times\) and short wavelength visible light is violet with 4 \(\times\) 10^-7m. The frequency range of visible light is between 400 to 790 THz. Visible light is used in communication.

Infrared radiation

It is a form of electromagnet radiation which is invisible to human eye. The wavelength of infrared radiation ranges from 10^-5m to 5 \(\times\) 10^-3m. We cannot see infrared radiation but we can feel due to its heat. The frequency range of infrared radiation is between 430THz to 300GHz. Infrared is used in night vision where the is not enough light. It is also used in tracking, heating, and communication. Sun also produced infrared radiation. We cannot see them as they are invisible but we feel hot or warm due the infrared radiation of the sun when we stay in sunlight.

Radio waves

Radio waves is a type of electromagnetic radiation. It is widely used in communication, in television, cell phones, radios, etc. It is used in the transmission of data in coded form. In the form of radar, it is used also for sending out signals and picking up their reflections from objects in their path. It has the longest wavelength among all the electromagnetic spectrum. The wavelength of radio waves ranges from 10^-4m to 5 \(\times\)10⁴m. It is produced by electrical oscillations and is detected by radio receivers or similar tuned circuits. The frequency of radio waves ranges from 300GHz to 3Hz.

Ultraviolet radiation

Ultraviolet radiation is a form of electromagnetic radiation with wavelength ranging from 5 \(\times\) 10^-9m to 5 \(\times\) 10^-7m. It has a shorter wavelength than visible light but longer than X- rays. It is present in the sun. It stimulates vitamin D production in our body but is harmful to eye and skin. In ozone layer, it produces ozone gas. UV radiation is widely used in industrial processes and in medical and dental practices for a variety of purposes, such as killing bacteria, creating fluorescent effects, curing inks and resins, phototherapy and suntanning.

X- rays andγ- rays

X- rays andγ- rays are electromagnetic radiation like radio waves, infrared radiation, ultraviolet radiation, etc. The wavelength of X-rays andγ- rays ranges below 5 \(\times\) 10^-8m. They are high energy electromagnetic radiation or are of high frequency.γ - rays are produced in radioactive decay and nuclear reaction. X- rays are produced by electrons. X- rays are used in hospitals for medical purpose. Gamma rays are used in medical field to cure cancer.

Difference between ultraviolet rays and x-rays

Ultraviolet rays	X-ray
Its average wavelength and frequency are 10^-8 and 10¹⁵ Hz respectively.	Its average wavelength and frequency are 10^-10 and 10¹⁸ Hz respectively.
It is obtained from sun, tube light etc.	It is obtained by x-ray machine.

Difference between ultraviolet rays and infrared rays.

Ultraviolet rays	Infrared rays
The frequency is high.	The frequency is low.
They have more energy.	They have less energy.
They are harmful.	They are not harmful.

Lesson

Light

Subject

Science

Grade

Grade 9

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