AmbifulWorksheets
Practice that never repeats
CBSE · Class 12 · Physics

Electromagnetic Waves

Standard difficulty · 20 questions · 40 marks

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
The wavelength of an electromagnetic wave of frequency 1 × 1011 Hz in vacuum is:
  1. 3 × 10−4 m
  2. 3 × 1019 m
  3. 0.03 m
  4. 3 × 10−3 m
2.
The electric field of an electromagnetic wave has amplitude 222 V/m. The amplitude of its magnetic field is:
  1. 7.4 × 10−7 T
  2. 6.66 × 1010 T
  3. 7.4 × 10−5 T
  4. 7.4 × 10−9 T
3.
Electromagnetic radiation of wavelength 450 nm is:
  1. microwaves
  2. radio waves
  3. gamma rays
  4. visible light
4.
Which electromagnetic waves are used for physical therapy by heating?
  1. infrared
  2. visible light
  3. ultraviolet
  4. gamma rays
5.
Maxwell added to Ampere's law a term called the:
  1. displacement current
  2. induced emf
  3. eddy current
  4. drift current
6.
Light travels at 2 × 108 m/s in a medium. Its refractive index is:
  1. 3
  2. 2/3
  3. 2
  4. 3/2
7.
The voltage across a 10 μF capacitor rises at 30 × 103 V/s. The displacement current between its plates is:
  1. 0.3 A
  2. 3 × 105 A
  3. 3.33 × 10−4 A
  4. 3 × 10−4 A
8.
Assertion (A): An electromagnetic wave of frequency 1 × 1012 Hz has a wavelength of 3 × 10−4 m in vacuum.
Reason (R): The wavelength of an electromagnetic wave equals its frequency divided by c.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
Section B — Short answer8 × 2 = 16 marks
9.
A radio station broadcasts at 102 MHz. Find the wavelength of its waves.
10.
The magnetic field of a plane electromagnetic wave has amplitude 30 × 10−8 T. Find the amplitude of its electric field.
11.
A 14 μF parallel-plate capacitor is being charged so that its voltage rises at 6 × 103 V/s. Find the displacement current between the plates and the conduction current in the wires.
12.
Name the region of each wavelength and arrange them in order of increasing frequency: 550 nm, 10 μm, 1 cm.
13.
A radio signal from a space probe 8 × 1012 m away travels to the Earth. How long does it take?
14.
Light of wavelength 560 nm in air enters a medium of refractive index 5/3. Find its speed, wavelength and frequency in the medium.
15.
(a) Which waves are used for studying crystal structure? (b) Which region does a wavelength of 10 m belong to?
16.
A wave has wavelength 4 × 10−9 m in vacuum. Find its frequency and name its region.
Section C — Word problems4 × 4 = 16 marks
17.
A plane electromagnetic wave of frequency 5 × 1012 Hz travels along x in vacuum, and its electric field amplitude is 51 V/m. Find its wavelength, its angular frequency, the amplitude of its magnetic field, and the direction of B if E is along y.
18.
A radar pulse returns 310 μs after it is sent. How far away is the aircraft? Which kind of wave does radar use, and why?
19.
A 17 μF capacitor with plates 1 mm apart is charged at a rate that makes its voltage rise by 34 × 103 V every second. Find the displacement current, the rate of change of the electric field between the plates, and explain why the magnetic field just outside the gap is the same as near the wires.
20.
Four waves have wavelengths 10 μm, 10−10 m, 1 cm, 10−13 m. Name each region, give one use of each, and list them from lowest to highest photon energy.
AmbifulWorksheets
Practice that never repeats
CBSE · Class 12 · Physics

Answer key

Electromagnetic Waves · AW-12P-EMW-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(d) 3 × 10−3 mλ = c/f
2(a) 7.4 × 10−7 TB0 = E0/c
3(d) visible lightvisible light: 400 nm to 700 nm
4(a) infrared—
5(a) displacement current—
6(d) 3/2n = c/v
7(a) 0.3 AI_d = ε0 dΦ_E/dt = C dV/dt
8(c) A is true, but R is false.A is true: λ = c/f = 3 × 108 ÷ (1 × 1012) = 3 × 10−4 m. R is false.
92.94 mλ = c/f = 3 × 108 ÷ (102 × 106)
1090 V/mE0 = cB0
11both 0.084 Athe displacement current equals the conduction current: C dV/dt
12550 nm: visible light; 10 μm: infrared; 1 cm: microwaves. Increasing frequency: 1 cm, 10 μm, 550 nmfrequency rises as wavelength falls
132.67 × 104 st = d/c = 8 × 1012 ÷ (3 × 108)
141.8 × 108 m/s; 336 nm; 5.36 × 1014 Hz (unchanged)v = c/n; λ = λ0/n; f stays the same
15(a) X-rays; (b) radio wavesradio waves: above 0.1 m
167.5 × 1016 Hz; X-raysf = c/λ; X-rays: 10−12 m to 10−8 m
176 × 10−5 m; 1 × 1013π rad/s; 1.7 × 10−7 T; along zλ = c/f; ω = 2πf; B0 = E0/c; E × B points along the direction of travel
184.65 × 104 m; microwaves, because their short wavelength reflects well from aircraft and they pass through cloudsdistance = ct/2 (there and back)
190.578 A; dE/dt = 3.4 × 107 V/(m s); the displacement current in the gap equals the conduction current in the wires, so Ampere–Maxwell gives the same fieldI_d = C dV/dt; E = V/d
2010 μm: infrared (TV remote controls and night vision); 10−10 m: X-rays (photographing broken bones); 1 cm: microwaves (radar and microwave ovens); 10−13 m: gamma rays (treating some cancers and sterilising food). Lowest to highest energy: 1 cm, 10 μm, 10−10 m, 10−13 menergy rises as wavelength falls