Uses of Each Type of EM Wave - UNSOLVED PRACTICE SET
Chapter: Electromagnetic Waves | Topic: Uses of Each Type of EM Wave
USES OF EACH TYPE OF EM WAVE - UNSOLVED PRACTICE SET
Topic: Uses of Each Type of EM Wave
Multiple Choice Questions
Q1. Radio waves are used for long-distance communication because:
- They have high energy
- They can be reflected by the ionosphere
- They are absorbed by the atmosphere
- They have very short wavelength
Q2. Microwave ovens heat food by:
- Ionizing food molecules
- Causing water molecules to resonate and rotate
- Producing X-rays inside the food
- Conduction of heat from the oven walls
Q3. Infrared radiation is used in:
- Cancer treatment
- Night vision devices and remote controls
- Sterilizing surgical instruments
- Detecting cracks in metal structures
Q4. Ultraviolet radiation is used for:
- Radio broadcasting
- Sterilization and detecting forged documents
- Cooking food
- Medical imaging of bones
Q5. X-rays are used in medical diagnosis because they:
- Are absorbed equally by all materials
- Can pass through soft tissues but are absorbed by bones
- Are completely reflected by the human body
- Cause fluorescence in all materials
Q6. Gamma rays are used in cancer treatment (radiotherapy) because:
- They have low penetrating power
- They can destroy cancer cells without damaging surrounding tissue (when precisely targeted)
- They are harmless to living cells
- They only affect healthy cells
Short Answer Questions
Q7. Why are radio waves used for communication while gamma rays are not? Give two reasons.
Q8. Explain how a microwave oven cooks food. Why does it heat water-containing food but not dry ceramic plates?
Q9. How are infrared cameras used in night vision? Explain the principle behind their working.
Q10. Why are X-rays used to detect fractures in bones but not recommended for frequent health check-ups?
Q11. How is ultraviolet radiation used to purify drinking water? What property of UV makes it suitable for this purpose?
Q12. Why are gamma rays used to sterilize medical equipment and food products? What advantage do they have over other methods?
Long Answer Questions
Q13. Describe the various applications of radio waves and microwaves in communication technology. Explain how different frequency bands are allocated for different uses (AM, FM, TV, mobile phones, satellite communication).
Q14. Discuss the medical and industrial applications of X-rays and gamma rays. Compare their uses, advantages, and potential hazards. How are these hazards minimized in practice?
Q15. Explain the applications of infrared, visible, and ultraviolet radiation in everyday life and technology. Discuss one application each where these radiations are beneficial and one where they can be harmful.
Numerical & Application-Based Problems
Q16. A mobile phone tower operates at a frequency of 900 MHz and radiates power of 20 kW uniformly in all directions.
(a) Calculate the wavelength of the radiation.
(b) Calculate the intensity of radiation at a distance of 2 km from the tower.
(c) A person standing at this distance receives radiation over a body surface area of 1.5 m² for 1 hour. Calculate the total energy received.
(d) Compare this energy with the energy received from the Sun in the same time (solar constant ≈ 1000 W/m²).
Q17. A microwave oven operates at 2.45 GHz with a power output of 800 W.
(a) Calculate the wavelength and energy of each photon.
(b) How many photons are emitted per second?
(c) A cup of water (250 g) at 20°C is heated in this oven for 2 minutes. Assuming all the microwave energy is absorbed by the water, calculate the final temperature of the water. (Specific heat capacity of water = 4200 J/kg·K)
(d) In practice, the final temperature is less than calculated. Suggest two reasons why.
Q18. In India, various technologies use different parts of the electromagnetic spectrum:
(a) ISRO uses radio waves to communicate with satellites. A signal is sent from a ground station at 2 GHz. Calculate the wavelength and explain why this frequency is chosen over much higher frequencies.
(b) Hospitals across India use X-ray machines for diagnostic imaging. An X-ray tube operates at 80 kV. Calculate the minimum wavelength of X-rays produced and explain why this 'hard' X-ray is suitable for imaging bones.
(c) During the COVID-19 pandemic, UV-C sterilization tunnels were set up in many Indian cities to disinfect objects. UV-C has a wavelength of about 254 nm. Calculate its photon energy and explain why it is effective at killing viruses and bacteria.
(d) A student sees an advertisement for a 'gamma ray phone charger' that claims to charge phones instantly using gamma rays. Using your knowledge of the EM spectrum, explain why this product is either a scam or extremely dangerous (or both).