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Transcript
(Q.1) Microwaves are electromagnetic waves with frequency, in the range of (A) Micro Hertz (B) Mega Hertz (C) Giga Hertz (D) Hertz (Q.2) Infrared radiation lies adjacent to the low frequency or long wavelength end of the visible spectrum. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the: (A) Energy it carries (B) Momentum it transferred (C) The way it heat up the surroundings (D) Greenhouse effect ( 1 mark ) ( 1 mark ) (Q.3) Give the formula for velocity of electromagnetic waves in free space? (Q.4) What are microwaves? ( 1 mark ) (Q.5) Who was the first person to tell that light is an electromagnetic wave? ( 1 mark ) (Q.6) What is the source of an electromagnetic wave? ( 1 mark ) (Q.7) What is the frequency limit of visible range of electromagnetic spectrum in Khz? (Q.8) What is the name given to that part of electromagnetic spectrum which is used in radar? (Q.9) Which of the following has shortest wavelength? Microwaves, ultraviolet rays and X-rays. ( 1 mark ) ( 1 mark ) ( 1 mark ) (Q.10) What is the ratio of speed of infrared rays to ultraviolet rays in vacuum? (Q.11) An electromagnetic wave is propagating along y-axis. What is the direction along which oscillations of magnetic field are taking place? (Q.12) Name the electromagnetic radiations used for viewing objects through haze and fog? (Q.13) What is the frequency of electromagnetic radiation to which the human eye is most sensitive? ( 1 mark ) ( 1 mark ) (Q.14) What is the role of ozone in the atmosphere? ( 1 mark ) (Q.15) What is the cut off frequency beyond which the ionosphere does not reflect electromagnetic radiations? ( 1 mark ) (Q.16) What is the ratio of speed of gamma rays and radiowaves in vacuum? ( 1 mark ) (Q.17) If e0and m0are the electric permittivity and magnetic permeability in vacuum, e and m are corresponding quantities in medium, then what is the refractive index of the medium? (Q.18) The energy of electromagnetic wave in vacuum is given by the relation: ( 1 mark ) ( 1 mark ) (A) (B) (C) (D) (Q.19) Let us consider an example of a plane electromagnetic wave propagating along z direction. The electric field E is along the x-axis and varies sinusoidally with z, at a given time. What is the direction of magnetic field ? (Q.20) When the sun shines on our hand, we feel the ( 1 mark ) ( 1 mark ) ( 1 mark ) ( 1 mark ) ( 1 mark ) energy being absorbed from electromagnetic waves, our hands get warm but we do not feel pressure. Why ? (Q.21) What is average magnetic field of the air plane a distance of 100 km from a radio transmitter receiving a signal of power 10.0 micro watts/m2? ( 1 mark ) (Q.22) Electric and magnetic fields oscillate sinusoidally in space and time in an electromagnetic wave. The oscillating electric and magnetic fields and are perpendicular to each other and to the direction of propagation of the electromagnetic wave. For a wave of frequency , wavelength propagating along z direction, E0 and B0 are related as: ( 1 mark ) , (A) (B) (C) (D) (Q.23) Which of the following law was modified by Maxwel introducing Maxwell displacement current? (Q.24) In an electromagnetic wave, the amplitudes of magnetic field Ho and electric field Eo in free space are related as: (A) H0 = Eo ( 1 mark ) ( 1 mark ) (B) (C) (D) (Q.25) Which of the following are not electromagnetic waves? (A) Cosmic rays (B) Gamma rays (C) -rays (D) X-rays (Q.26) Transmission via sky waves is impossible for the frequencies: (A) less than 40 MHz (B) equal to 40 MHz (C) more than 40 MHz (D) all of these ( 1 mark ) ( 1 mark ) (Q.27) In an apparatus, the electric field was found to oscillate with amplitude of 18 V/m. what is the magnitude of the oscillating magnetic field? ( 1 mark ) (Q.28) The missing term in Ampere’s circuital law is: ( 1 mark ) (A) (B) (C) (D) (Q.29) Which of the following term acts as a source of magnetic field in exactly the same way as conduction current? (A) ( 1 mark ) (B) (C) (D) (Q.30) In the case of steady electric fields in a conducting wire, which of the following quantity is zero ? (A) Conduction current (B) Magnetic current (C) Magnetic lines of forces (D) Displacement current (Q.31) What is the source of electromagnetic waves? (A) Stationary charges (B) Charges in uniform motion (C) Accelerated charges (D) Varrying magnetic field (Q.32) What is the average electric field at the airplane flying at a distance of 100 km from a radio transmitter receiving a signal of power 10.0 micro watts/m2 ? (A) 8.68 ×10–2 V/m (B) 6.14 ×10–1 V/m (C) 86.8 ×10–2 V/m (D) 6.14 ×10–2 V/m View Answer (Q.33) A parallel plate capacitor made of circular plates each of radius R = 5 cm has a capacitance C = 100 pF. The capacitor is connected to a 220 V a.c supply with angular frequency of 295 rad s–1. What is the rms value of the conduction current ? ( 1 mark ) ( 1 mark ) ( 1 mark ) ( 1 mark ) (A) (B) (C) (D) View Answer (Q.34) The dimensions of E/B are same as that of: (A) Acceleration (B) Velocity (C) Charge (D) Current View Answer (Q.35) In case of microwave oven, which material is used as vessels ? (A) Metal (B) Steel (C) Porcelain (D) Copper View Answer (Q.36) The microwave oven has an advantage over conventional heating method as in microwave oven: (A) Energy is not wasted in heating up the vessel (B) Porcelain has been used as vessel (C) Microwave radiation has been used as source (D) Special vacuum tubes have been used View Answer (Q.37) Infrared band lies adjacent to the low-frequency or long-wavelength end of the visible spectrum. Infrared waves are sometimes referred to as: (A) Low-frequency waves (B) Heat waves (C) Long-wavelength waves (D) Electromagnetic waves View Answer (Q.38) The spectrum of electromagnetic wave stretches over an infinite range of wavelengths. Different regions are known by different names. The basic difference lies in their: (A) Atoms or molecules (B) Wavelengths or frequencies (C) Electric or magnetic field (D) Difference in frequencies with visible light View Answer (Q.39) A T.V. tower has a height of 100 m. How much population is covered by the T.V. broadcast if the average population density around the tower is 10000 km–2? Radius of the earth = 6.40 × 106 m (A) 40.19 lakhs (B) 4 lakhs (C) 40192 lakhs ( 1 mark ) ( 1 mark ) ( 1 mark ) ( 1 mark ) ( 1 mark ) ( 1 mark ) (D) 402 lakhs View Answer (Q.40) An electromagnetic wave of frequency passes from vacuum into a dielectric ( 1 mark ) medium with permittivity . Then (A) Wavelength is halved and frequency remains unchanged (B) Wavelength is doubled and frequency becomes half (C) Wavelength is doubled and the frequency remains unchanged (D) Wavelength and frequency both remain unchanged. View Answer (Q.41) Radio waves of constant amplitude can be generated with (A) Filter (B) Rectifier (C) FET (D) Oscillator View Answer (Q.42) The area to be covered for T.V. telecast is doubled then the height of transmitting antenna will have to be (A) Halfed (B) Doubled (C) Quardupled (D) Kept unchanged View Answer (Q.43) The electric field vector of a plane electromagnetic wave oscillates sinusoidally at a frequency of 4.5 x 1010 Hz. What is the wavelength? View Answer (Q.44) Find the wavelength of electromagnetic waves of frequency 5x1019 Hz in free space. Give its two applications. View Answer (Q.45) Why is it necessary to use satellite for long distance T.V. transmission? Give reasons. View Answer (Q.46) Give four properties of electromagnetic waves. View Answer (Q.47) A plane electromagnetic wave travels, in vacuum, along the Y-direction. Write the, (i) Ratio of the magnitudes of electric and magnetic field. (ii) The directions of its electric and magnetic field vectors. View Answer (Q.48) Sky waves are not used in transmitting TV signals. Why? State two factors by which the range of transmission of TV signals can be increased. View Answer (Q.49) Explain the following terms: a) Ground waves. b) Space waves. c) Sky waves. View Answer (Q.50) The TV transmission tower at particular station has a height of 120 m. a) What is its covering range? b) By how much the height of tower should be increased to double its coverage range? View Answer (Q.51) What is “Greenhouse effect” for the atmosphere of earth? Write its importance. View Answer ( 1 mark ) ( 1 mark ) ( 2 Marks ) ( 2 Marks ) ( 2 Marks ) ( 2 Marks ) ( 2 Marks ) ( 2 Marks ) ( 3 Marks ) ( 3 Marks ) ( 3 Marks ) (Q.52) Suppose that the electric field part of an electromagnetic wave in vacuum is ={(3.1 N/C) cos [(1.8 rad/m) y + (5.4 × 106 rad/s)t]} . (a) What is the direction of propagation? (b) What is the wavelength λ ? (c) What is the frequency ν ? (d) What is the amplitude of the magnetic field part of the wave? ( 5 Marks ) (e) Write an expression for the magnetic field part of the wave. View Answer (Q.53) Suppose that the electric field part of an electromagnetic wave in vacuum is [(1.8 rad/m) y + (5.4 × 106 ={(3.1 N/C) cos rad/s)t]} . (a) What is the direction of propogation? (b) What is the wavelength λ ? (c) What is the frequency ν ? (d) What is the amplitude of the magnetic field part of the wave? (e) Write an expression for the magnetic field part of the wave. View Answer ( 5 Marks )