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CodeVID-P12-04-EMS-01
The Electromagnetic Spectrum — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The band with the highest frequency is:
- A.radio
- B.infrared
- C.X-ray
- D.gamma ray
2.
Infrared radiation is commonly associated with:
- A.heat
- B.sterilisation
- C.vision
- D.RADAR
3.
X-rays are produced by:
- A.hot bodies
- B.oscillating antenna currents
- C.fast electrons hitting a metal target
- D.radioactive nuclei
4.
The order of increasing frequency is:
- A.radio, IR, visible, X-ray
- B.X-ray, visible, IR, radio
- C.visible, radio, IR, X-ray
- D.IR, radio, X-ray, visible
5.
Ozone in the atmosphere mainly protects us by absorbing:
- A.radio waves
- B.ultraviolet
- C.infrared
- D.microwaves
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
A TV signal has frequency $200\ \text{MHz}$. Find its wavelength.
7.
Name the source and one use of microwaves.
8.
Why are gamma rays more dangerous than radio waves?
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Red light has $\lambda=700\ \text{nm}$ and violet light $\lambda=400\ \text{nm}$. Find their frequencies and state which has higher photon energy.
10.
List, in order of increasing frequency, the seven main bands of the EM spectrum and give one use of each.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe the electromagnetic spectrum from radio to gamma rays. State for each band its approximate wavelength range, how it is produced, and one important use.
Answer Key
Section A — Multiple Choice Questions
- (D) gamma ray
- (A) heat
- (C) fast electrons hitting a metal target
- (A) radio, IR, visible, X-ray
- (B) ultraviolet
Section B — Short Answer (2 marks)
- $\lambda=\frac{c}{f}=\frac{3\times10^{8}}{200\times10^{6}}=1.5\ \text{m}$.
- Source: klystron/magnetron vacuum tubes. Use: RADAR, satellite/mobile communication, microwave ovens.
- Gamma rays have far higher frequency and photon energy ($E=hf$), so they are highly penetrating and ionising, while low-energy radio waves are not.
Section C — Short Answer (3 marks)
- Red: $f=\frac{3\times10^{8}}{700\times10^{-9}}\approx4.29\times10^{14}\ \text{Hz}$; Violet: $f=\frac{3\times10^{8}}{400\times10^{-9}}=7.5\times10^{14}\ \text{Hz}$. Violet has higher frequency, hence higher photon energy.
- Radio (broadcasting), microwave (RADAR/ovens), infrared (night vision), visible (sight), ultraviolet (sterilisation), X-ray (imaging), gamma (radiotherapy).
Section D — Long Answer (5 marks)
- Radio ($\lambda>0.1\ \text{m}$, antennas, broadcasting); microwave ($1\ \text{mm}$–$0.1\ \text{m}$, klystron/magnetron, RADAR/ovens); infrared ($700\ \text{nm}$–$1\ \text{mm}$, hot bodies, night vision/remotes); visible ($400$–$700\ \text{nm}$, atoms/hot bodies, sight); ultraviolet ($10$–$400\ \text{nm}$, hot bodies/UV lamps, sterilisation); X-ray ($0.01$–$10\ \text{nm}$, fast electrons on metal, medical imaging); gamma ($<0.01\ \text{nm}$, radioactive nuclei, cancer therapy). All travel at $c$ with $c=f\lambda$.
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