Title 08. ELECTROMAGNETIC WAVES.pdf ✅

BUY COURSE FROM STORE TO GET INSTANT ANSWER AND EXPLANATION OF EACH QUESTION SPARK PCMB | DOWNLOAD APP NOW| +91-920-630-6398 08. ELECTROMAGNETIC WAVES #QID# 31867 (1.) In an electromagnetic wave, the electric and magnetizing fields are 100 Vm−1 and 0.265 Am−1 . The maximum energy flow is (a.) 26.5 Wm−2 (b.) 36.5 Wm−2 (c.) 46.7 Wm−2 (d.) 765 Wm−2 Ans: a Exp: (a) Here, amplitude of electric filed, E0 = 100 Vm−1 ; amplitude of magnetic field, B0 = 0.265 Am−1 . We know that the maximum rate of energy flow S = E0 × B0 = 100 × 0.265 = 26.5 Wm−2 #QID# 31868 (2.) X-ray are not used for radar purpose, because they are not (a.) Reflected by target (b.) Partly absorbed by target (c.) Electromagnetic waves (d.) Completely absorbed by target Ans: a Exp: (a) X-rays being of high energy radiations, penetrate the target and hence are not reflected back #QID# 31869 (3.) If an electromagnetic wave is propagation in a medium with permittivity ε and permittivity μ, then √ μ ε is the (a.) Intrinsic impedance of the medium (b.) Square of the refractive index of the medium
BUY COURSE FROM STORE TO GET INSTANT ANSWER AND EXPLANATION OF EACH QUESTION SPARK PCMB | DOWNLOAD APP NOW| +91-920-630-6398 (c.) Refractive index of the medium (d.) Energy density of the medium Ans: a Exp: (a) √ μ ε = has the dimensions of resistance, hence it is called the intrinsic impedance of the medium #QID# 31870 (4.) An earth orbiting satellite has solar energy collecting panel with total area 5 m2 . If solar radiations are perpendicular and completely absorbed, the average force associated with the radiation pressure is (Solar constant= 1.4 kWm−2 ) (a.) 2.33 × 10−3 N (b.) 2.33 × 10−4 N (c.) 2.33 × 10−5 N (d.) 2.33 × 10−6 N Ans: c Exp: (c) Power = I × area = (1.4 × 103 ) × 5 Force F = Power c = 1.4×103 ×5 3×108 = 2.33 × 10−5 N #QID# 31871 (5.) For EM wave prorogating along x-axis, Emax = 30 Vm−1 . what is maximum value of magnetic field? (a.) 10-7 T (b.) 10-8 T (c.) 10-9 T (d.) 10-6 T Ans: a Exp: (a)
BUY COURSE FROM STORE TO GET INSTANT ANSWER AND EXPLANATION OF EACH QUESTION SPARK PCMB | DOWNLOAD APP NOW| +91-920-630-6398 The amplitude of the electric and magnetic fields in free space are related by E0 B0 = c Here, E0 = 30 Vm−1 , c = 3 × 108 ms−1 ∴ B0 = E0 c = 30 3 × 108 = 10−7 T #QID# 31872 (6.) A parallel plate capacitor is charged to60μC. Due to a radioactive source, the plate loss charge at the rate of 1.8 × 10−8 Cs−1 . The magnitude of displacement current is (a.) 1.8 × 10 −8 Cs −1 (b.) 3.6 × 10−8Cs−1 (c.) 4.1 × 10−11Cs−1 (d.) 5.7 × 10−12 Cs−1 Ans: a Exp: (a) Displacement current is given by Id = dq dt = 1.8 × 10−8 Cs−1 #QID# 31873 (7.) If ε0 and μ0 are the electric permittivity and magnetic permeability of free space and ε and μ are the corresponding quantities in the medium, the index of refraction of the medium in terms of above parameter is (a.) εμ ε0μ0 (b.) ( εμ ε0μ0 ) 1/2 (c.) ( ε0μ0 εμ ) (d.) ( ε0μ0 εμ ) 1/2 Ans: b Exp: (b) Velocity of light in vacuum
BUY COURSE FROM STORE TO GET INSTANT ANSWER AND EXPLANATION OF EACH QUESTION SPARK PCMB | DOWNLOAD APP NOW| +91-920-630-6398 c = 1 √μ0ε0 velocity of light in medium v = 1 √μ ε ∴ μ = c v = ( με μ0ε0 ) 1/2 #QID# 31874 (8.) According to Maxwell’s hypothesis, a changing electric field gives rise to (a.) An emf (b.) Electric current (c.) Magnetic field (d.) Pressure radiant Ans: c Exp: (c) According to Maxwell, a changing electric field is a source of magnetic field #QID# 31875 (9.) Electric fields induced by changing magnetic fields are (a.) Conservation (b.) Non-conservation (c.) May be conservative or non-conservation depending on the conditions (d.) Nothing can be said Ans: b Exp: (b) The electric field induced by changing magnetic field depends upon the rate of change of magnetic flux, hence it is non-conservative #QID# 31876 (10.) The electric field of a plane electromagnetic wave varies with time of amplitude 2 Vm-1 propagating along z-axis. The average energy density of the magnetic field is (in Jm−3) (a.) 13.29 × 10−12