Title ELECTROMAGNETIC WAVES.pdf ✅

CHAPTER 8 ELECTROMAGNETIC WAVES Exercise 1: NCERT Based Topic-wise MCQs 8.1 INTRODUCTION 1. Speed of eletromagnetic wave in free space is NCERT Page-270 / N-201 (a) 1 × 108m/s (c) 3 × 108m/s (b) 2 × 108m/s (d) 4 × 108m/s 8.2 DISPLACEMENT CURRENT 2. The current in the electric circuit which arises due to flow of electrons in the connecting wires of the circuit in a defined closed path is called NCERT Page-270 / N-202 (a) alternating current (b) direct current (c) conduction current (d) displacement current 3. If a variable frequency ac source connected to a capacitor then with decrease in frequency, the displacement current will NCERT Page-270 / N-202 (a) increase (b) decrease (c) remain constant (d) first decrease then increase 4. An instantaneous displacement current of 1A can be set up by changing the potential difference across the parallel plates capacitor (1.0μF) at the rate of dV dt. NCERT Page-271 / N-203 here dV dt is (a) 106Vs−1 (b) 103Vs−1 (c) 102Vs−1 (d) 101Vs−1 5. Displacement current goes through the gap between the plates of a capacitor when the charge on the capacitor (a) is changing with time NCERT Page-271 / N-203 (b) decreases (c) does not change (d) decreases to zero 6. According to Maxwell's hypothesis, a changing electric field gives rise to NCERT Page-271 / N-204 (a) an e.m.f
(b) electric displacement current (c) magnetic field (d) pressure gradient 7. Displacement current is NCERT Page-270 / N-202 (a) continuous when electric field is changing in the circuit (b) continuous when magnetic field is changing in the circuit (c) continuous in both types of fields (d) continuous through wires and resistance only 8. Maxwell's modified form of Ampere's circuital law is NCERT Page-273 / N-204 (a) ∮ s B⃗ ⋅ ⃗ds⃗⃗⃗ = 0 (b) ∮ s B⃗ ⋅ dl ⃗⃗⃗ = μ0I (c) ∮ s B⃗ ⋅ dl ⃗⃗⃗ = μ0I + 1 εo dq dt (d) ∮ s B⃗ ⋅ dl ⃗⃗⃗ = μ0I + μ0εo dφE dt 9. When an electromagnetic waves enter the ionised layer of ionosphere, the motion of electron cloud produces a space current and the electric field has its own capacitative displacement current, then NCERT Page-271 / N-203 (a) the space current is in phase of displacement current (b) the space current lags behind the displacement current by a phase 180∘ . (c) the space current lags behind the displacement current by a phase 90∘ . (d) the space current leads the displacement current by a phase 90∘ . 10. In order to establish an instantaneous displacemet current of 5mA in the space between the plates of 5μF parallel plate capacitor, the potential difference need to apply is NCERT Page-271 / N-203 (a) 100Vs−1 (b) 200Vs−1 (c) 300Vs−1 (d) 1000Vs−1 11. A circular ring of radius r is placed in a homogeneous magnetic field perpendicular to the plane of the ring. The field B changes with time according to equation B = kt, where, k is a constant and t is the time). The electric field in the ring is: NCERT Page-273 / N-205 (a) kr 4 (b) kr 3 (c) kr 2 (d) k 2r 12. The magnetic field between the plates of radius 12cm separated by distance of 4mm of a parallel plate capacitor of capacitance 100pF along the axis of plates having conduction current of 0.15A is NCERT Page-272/N-203 (a) zero (b) 1.5T (c) 15T (d) 0.15T 13. The charge on a parallel plate capacitor varies as q = q0cos 2πvt. The plates are very large and close together ( area = A, separation = d). Neglecting the edge effects, the displacement current through the capacitor is (a) 2πvq0sin 2πvt NCERT Page-271 / N-203 (b) 3/5πvq0sin πvt (c) 4πvq0sin 2πvt (d) None of these
14. A parallel plate capacitor with a and seperation d, is charged by a constant current I. Consider a plane surface of area a 2 parallel to the plates and drawn symmetrically between the plates. What is the displacement current through this area? NCERT Page-271 / N-203 (a) I/2 (b) I/3 (c) I/5 (d) 1/7 8.3 ELECTROMAGNETIC WAVES 15. The magnetic field of a plane electromagnetic wave is given by: NCERT Page-275 / N-207 B⃗ = 2 × 10−8 sin (0.5 × 103x + 1.5 × 1011t)jˆT. The amplitude of the electric field would be: (a) 6Vm−1 along x-axis (b) 3Vm−1 along z-axis (c) 6Vm−1 along z-axis (d) 2 × 10−8Vm−1 along z-axis 16. In an electromagnetic wave, the direction of the magnetic induction B⃗ is NCERT Page-275 / N-206 (a) parallel to the electric field E⃗ (b) perpendicular to the electric field E⃗ (c) antiparallel to the Poynting vector S⃗ (d) random 17. The polarisation of electromagnetic wave is in NCERT Page-274 / N-205 (a) the directions of electric and magnetic field (b) the directions of electric field (c) the direction of magnetic field (d) can not be polarized 18. In an electromagnetic wave NCERT Page-275 / N-206 (a) power is transmitted along the magnetic field (b) power is transmitted along the electric field (c) power is equally transferred along the electric and magnetic fields (d) power is transmitted in a direction perpendicular to both the fields 19. If the frequency of EM radiations is halved then the energy of EM radiation will become (a) double NCERT Page-274 / N-206 (b) remains unchanged (c) becomes half (d) becomes one fourth 20. Select the wrong statement. EM waves NCERT Page-274 / N-206 (a) are transverse in nature. (b) travel in free space at a speed of light. (c) are produced by accelerating charges (d) travel in all media with same speed. 21. Which of the following has/have zero average value in a plane electromagnetic wave? (a) Both magnetic and electric field NCERT Page-276 / N-206 (b) Electric field only (c) Magnetic energy (d) Electric energy
22. The electromagnetic waves NCERT Page-274 / N-207 (a) travel with the speed of sound (b) travel with the same speed in all media (c) travel in free space with the speed of light (d) do not travel through a medium 23. An electromagnetic wave propagating along north has its electric field vector upwards. Its magnetic field vector point towards NCERT Page-275 / N-206 (a) north (b) east (c) west (d) downwards 24. A plane electromagnetic wave is incident on a material surface. If the wave delivers momentum p and energy E, then NCERT Page-275 / N-206 (a) p = 0, E = 0 (b) p ≠ 0, E ≠ 0 (c) p ≠ 0, E = 0 (d) p = 0, E ≠ 0 25. The oscillating electric and magnetic vectors of an electromagnetic wave are oriented along (a) the same direction but differ in phase by 90∘ NCERT Page-276 / N-206 (b) the same direction and are in phase (c) mutually perpendicular directions and are in phase (d) mutually perpendicular directions and differ in phase by 90∘ 26. The oscillating magnetic field in a plane electromagnetic wave is given by By = 5 × 10−6 sin 1000π(5x − 4 × 108 t)T. The amplitude of electric field will be : NCERT Page-276 / N-207 (a) 15 × 102Vm−1 (b) 5 × 10−6Vm−1 (c) 16 × 1012Vm−1 (d) 4 × 102Vm−1 27. The magnetic field in a travelling electromagnetic wave has a peak value of 20nT. The peak value of electric field strength is NCERT Page-276 / N-207 (a) 3V/m (b) 6V/m (c) 9V/m (d) 12V/m 28. In a plane electromagnetic wave propagating in space has an electric field of amplitude 9 × 103V/m, then the amplitude of the magnetic field is NCERT Page-276 / N-207 (a) 2.7 × 1012T (b) 9.0 × 10−3T (c) 3.0 × 10−4T (d) 3.0 × 10−5T 29. A beam has intensity 2.5 × 1014Wm−2 . The ratio of electric and magnetic fields in the beam is (a) 2.98 × 108NC−1T −1 NCERT Page-277 / N-207 (b) 8.32 × 105NCT−1 (c) 6.22 × 107NC−1T −1 (d) 2.88 × 106NCT−1 30. An electromagnetic wave passes through space and its equation is given by E = E0sin (ωt − kx) where E is electric field. Energy density of electromagnetic wave in space is NCERT Page-277 / N-207