Practice Questions

Q16.The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0. 710 V. When the incident wavelength is changed to a new value, the stopping potential is 1. 43 V. The new wavelength is : (1) 382 nm (2) 309 nm (3) 329 nm (4) 400 nm

Q16.A plane electromagnetic wave propagating along y-direction can have the following pair of electric field (→E) and magnetic field components. (→B) (1) Ey, By or Ez, Bz (2) Ey, Bx or Ex, By (3) Ex, Bz or Ez, Bx (4) Ex, By or Ey, Bx

Q16.An object is placed beyond the centre of curvature C of the given concave mirror. If the distance of the object is d1 from C and the distance of the image formed is d2 from C, the radius of curvature of this mirror is: (1) 2 d1 d2 (2) 2 d1 d2 d1+d2 d1−d2 (3) d1 d2 (4) d1 d2 d1+d2 d1−d2

Q16.The de Broglie wavelength of a proton and α -particle are equal. The ratio of their velocities is (1) 4 : 1 (2) 4 : 3 (3) 1 : 4 (4) 4 : 2

Q16.The de-Broglie wavelength associated with an electron and a proton were calculated by accelerating them through same potential of 100 V . What should nearly be the ratio of their wavelengths ? ( mp = 1. 00727 u, me = 0. 00055 u) (1) 1860 : 1 (2) (1860)2 : 1 (3) 41. 4 : 1 (4) 43 : 1

Q16.A particle of mass 4𝑀 at rest disintegrates into two particles of mass 𝑀 and 3𝑀, respectively, having non zero velocities. The ratio of de-Broglie wavelength of particle of mass 𝑀 to that of mass 3𝑀 will be: (1) 1: 3 (2) 3: 1 (3) 1: √3 (4) 1: 1

Q16.Curved surfaces of a plano-convex lens of refractive index μ1 and a plano-concave lens of refractive index μ2 have equal radius of curvature as shown in figure. Find the ratio of radius of curvature to the focal length of the combined lenses (1) 1 (2) 1 μ2−μ1 μ1−μ2 (3) μ2 −μ1 (4) μ1 −μ2

Q16.An α particle and a proton are accelerated from rest by a potential difference of 200 V . After this, their de Broglie wavelengths are λα and λp respectively. The ratio λαλp is : (1) 8 (2) 3. 8 (3) 2. 8 (4) 7. 8

Q16.An oil drop of the radius 2 mm with a density 3 g cm−3 is held stationary under a constant electric field 3. 55 × 105 V m−1 in the Millikan's oil drop experiment. What is the number of excess electrons that the oil drop will possess? (consider g = 9. 81 m s−2). (1) 48. 8 × 1011 (2) 1. 73 × 1010 (3) 17. 3 × 1010 (4) 1. 73 × 1012

Q16.A square loop of side 20 cm and resistance 1 Ω is moved towards right with a constant speed 𝑣0 . The right arm of the loop is in a uniform magnetic field of 5 T . The field is perpendicular to the plane of the loop and is going into it. The loop is connected to a network of resistors each of value 4Ω . What should be the value of 𝑣0 so that a steady current of 2 mA flows in the loop ? JEE Main 2021 (01 Sep Shift 2) JEE Main Previous Year Paper (1) 10-2 cm s-1 (2) 1 m s-1 (3) 1 cm s-1 (4) 102 m s-1

Q16.A light beam is described by E = 800 sin ω(t −xc ). An electron is allowed to move normal to the propagation of light beam with a speed of 3 × 107 m s−1 . What is the maximum magnetic force exerted on the electron? (1) 1. 28 × 10−21 N (2) 12. 8 × 10−18 N (3) 1. 28 × 10−18 N (4) 12. 8 × 10−17 N JEE Main 2021 (26 Aug Shift 2) JEE Main Previous Year Paper

Q16.Given below are two statements : one is labeled as Assertion A and the other is labeled as Reason R. Assertion A : For a simple microscope, the angular size of the object equals the angular size of the image. Reason R: Magnification is achieved as the small object can be kept much closer to the eye than 25 cm and hence it subtends a large angle. In the light of the above statements, choose the most appropriate answer from the options given below: (1) A is false but R is true (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) Both A and R are true and R is the correct explanation of A →

Q16.An electron of mass m and a photon have same energy E. The ratio of wavelength of electron to that of photon is : ( c being the velocity of light) (1) 1 2m 21 (2) 1 E 12 c ( E ) c ( 2m ) (3) E 21 (4) c(2mE) 12 ( 2 m )

Q16.A ray of light passes from a denser medium to a rarer medium at an angle of incidence i. The reflected and refracted rays make an angle of 90° with each other. The angle of reflection and refraction are respectively r and r′. The critical angle is given by, JEE Main 2021 (22 Jul Shift 1) JEE Main Previous Year Paper (1) sin−1(cot r) (2) tan−1(sin i) (3) sin−1(tanr′) (4) sin−1(tan r)

Q16.Two plane mirrors M1 and M2 are at right angle to each other shown. A point source P is placed at a and 2a meter away from M1 and M2 respectively. The shortest distance between the images thus formed is : (Take √5 = 2. 3) (1) 2. 3 a (2) 2√10a (3) 4. 6a (4) 3a

Q16.In the given figure, a battery of emf E is connected across a conductor PQ of length l and different area of cross-sections having radii r1 and r2(r2 < r1). Choose the correct option as one moves from P to Q. (1) Drift velocity of electron increases. (2) Electric field decreases. (3) Electron current decreases. (4) All of these

Q16.A plane electromagnetic wave of frequency 500 MHz is traveling in a vacuum along the y−direction. At a → particular point in space and time, B = 8. 0 × 10−8ˆz T. The value of the electric field at this point is:(speed of light = 3 × 108 ms−1 ) ˆx, ˆy,ˆz are unit vectors along x, y and z direction. (1) −24ˆx V m−1 (2) 2. 6ˆx V m−1 (3) 24ˆx V m−1 (4) −2. 6ˆx V m−1 JEE Main 2021 (16 Mar Shift 1) JEE Main Previous Year Paper

Q16.A 10 Ω resistance is connected across 220 V −50 Hz AC supply. The time taken by the current to change from its maximum value to the rms value is: (1) 2. 5 ms (2) 1. 5 ms (3) 3. 0 ms (4) 4. 5 ms

Q16.The focal length 𝑓 is related to the radius of curvature 𝑟 of the spherical convex mirror by: 1 1 (1) 𝑓= - 2𝑟 (2) 𝑓= + 2𝑟 (3) 𝑓= 𝑟 (4) 𝑓= - 𝑟

Q16.Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : An electron microscope can achieve better resolving power than an optical microscope. Reason R : The de Broglie's wavelength of the electrons emitted from an electron gun is much less than wavelength of visible light. In the light of the above statements, choose the correct answer from the options given below: (1) A is false but R is true. (2) Both A and R are true and R is the correct explanation of A (3) Both A and R are true but R is NOT the correct (4) A is true but R is false. explanation of A

Q16.Region I and II are separated by a spherical surface of radius 25 cm. An object is kept in region I at a distance of 40 cm from the surface. The distance of the image from the surface is: (1) 55. 44 cm (2) 9. 52 cm (3) 18. 23 cm (4) 37. 58 cm

Q17.A particular hydrogen like ion emits radiation of frequency 2. 92 × 1015 Hz when it makes transition from n = 3 to n = 1. The frequency in Hz of radiation emitted in transition from n = 2 to n = 1 will be: (1) 6. 57 × 1015 (2) 2. 46 × 1015 (3) 0. 44 × 1015 (4) 4. 38 × 1015

Q17.Find the distance of the image from object O, formed by the combination of lenses in the figure: JEE Main 2021 (27 Aug Shift 1) JEE Main Previous Year Paper (1) 75 cm (2) 10 cm (3) infinity (4) 20 cm

Q17.Two identical photocathodes receive the light of frequencies f1 and f2 respectively. If the velocities of the photo-electrons coming out are v1 and v2 respectively, then (1) v21 −v22 = 2mh [f1 −f2] (2) v21 + v22 = 2hm [f1 + f2] (3) 2 h 21 (4) 2 h 21 v1 + v2 = [ m (f1 + f2)] v1 −v2 = [ m (f1 −f2)]

Q17.Three rays of light, namely red (R), green (G) and blue (B) are incident on the face PQ of a right angled prism PQR as shown in figure. The refractive indices of the material of the prism for red, green and blue wavelength are 1. 27, 1. 42 and 1. 49 respectively. The colour of the ray(s) emerging out of the face PR is : (1) green (2) red (3) blue and green (4) blue