Practice Questions

Q27.The frequency of a car horn encountered a change from 400 Hz to 500 Hz . When the car approaches a vertical wall. If the speed of sound is 330 m s−1 . Then the speed of car is ___ km h−1 .

Q27.A point source of light S , placed at a distance 60 cm infront of the centre of a plane mirror of width 50 cm, hangs vertically on a wall. A man walks infront of the mirror along a line parallel to the mirror at a distance 1. 2 m from it (see in the figure). The distance between the extreme points where he can see the image of the light source in the mirror is__ cm

Q27.A uniform conducting wire of length is 24a, and resistance R is wound up as a current carrying coil in the shape of an equilateral triangle of side a and then in the form of a square of side a . The coil is connected to a voltage source V0. The ratio of magnetic moment of the coils in case of equilateral triangle to that for square is 1 : √y where y is ____________. + A . The R.M.S. value of this current is

Q27.A certain metallic surface is illuminated by monochromatic radiation of wavelength λ . The stopping potential for photoelectric current for this radiation is 3 V 0. If the same surface is illuminated with a radiation of wavelength 2λ, the stopping potential is V0. The threshold wavelength of this surface for photoelectric effect is___________ λ.

Q27.A parallel plate capacitor has plate area 100 m2 and plate separation of 10 m. The space between the plates is filled up to a thickness 5 m with a material of dielectric constant of 10 . The resultant capacitance of the system is x pF. The value of ε0 = 8. 85 × 10−12 F m−1 . The value of x to the nearest integer is ______.

Q27.A cylindrical wire of radius 0. 5 mm and conductivity 5 × 107 S m−1 is subjected to an electric field of 10 mV m−1. The expected value of current in the wire will be x3π mA. The value of x is _________.

Q27.A parallel plate capacitor whose capacitance C is 14 pF is charged by a battery to a potential difference V = 12 V between its plates. The charging battery is now disconnected and a porcelain plate with k = 7 is inserted between the plates, then the plate would oscillate back and forth between the plates with a constant mechanical energy of _______ pJ. (Assume no friction)

Q27.In a series LCR resonant circuit, the quality factor is measured as 100 . If the inductance is increased by two fold and resistance is decreased by two fold, then the quality factor after this change will be _______

Q27.In the given figure the magnetic flux through the loop increases according to the relation ϕB(t) = 10t2 + 20t , where ϕB is in milliwebers and t is in seconds. The magnitude of current through R = 2 Ω resistor at t = 5 s is _____ mA.

Q27.The value of aluminium susceptibility is 2 . 2 × 10-5. The percentage increase in the magnetic field if space 𝑥 within a current carrying toroid is filled with aluminium is 104. Then the value of 𝑥 is

Q27.Consider a 72 cm long wire AB as shown in the figure. The galvanometer jockey is placed at P on AB at a distance x cm from A . The galvanometer shows zero deflection. JEE Main 2021 (18 Mar Shift 2) JEE Main Previous Year Paper The value of x, to the nearest integer, is

Q27.A steel rod with 𝑦= 2 . 0 × 1011 N m-2 and 𝛼= 10-5 ∘C of length 4 m and area of cross-section 10 cm2 is heated from 0°C to 400°C without being allowed to extend. The tension produced in the rod is JEE Main 2021 (01 Sep Shift 2) JEE Main Previous Year Paper 𝑥× 105 N where the value of 𝑥 is _________ .

Q27.A circular coil of radius 8. 0 cm and 20 turns is rotated about its vertical diameter with an angular speed of 50 rad s−1 in a uniform horizontal magnetic field of 3. 0 × 10−2 T . The maximum emf induced in the coil will be _______ ×10−2 volt (rounded off to the nearest integer).

Q28.A radioactive sample has an average life of 30 ms and is decaying. A capacitor of capacitance 200 μF is first charged and later connected with resistor R. If the ratio of the charge on the capacitor to the activity of the radioactive sample is fixed with respect to time then the value of R should be _______Ω.

Q28.The nuclear activity of a radioactive element becomes ( 81 ) th radioactive element is ________ years.

Q28.A circular conducting coil of radius 1 m is being heated by the change of magnetic field →𝐵 passing perpendicular to the plane in which the coil is laid. The resistance of the coil is 2 μΩ. The magnetic field is slowly switched off such that its magnitude changes in time as 4 𝑡 𝐵= 𝜋× 10-3 𝑇1 - 100 The energy dissipated by the coil before the magnetic field is switched off completely is 𝐸= ______mJ.

Q28.Seawater at a frequency f = 9 × 102 Hz , has permittivity ε = 80ε0 and resistivity ρ = 0. 25 Ω m . Imagine a parallel plate capacitor is immersed in seawater and is driven by an alternating voltage source V (t) = V0 sin(2πft). Then the conduction current density becomes 10x times the displacement current density after time t = 8001 s. The value of x is _______ (Given : 1 = 9 × 109 N m2 4πε0 C−2)

Q28.A square-shaped wire with a resistance of each side 3 Ω is bent to form a complete circle. The resistance between two diametrically opposite points of the circle in a unit of Ω will is, _____.

Q28.The electric field in a plane electromagnetic wave is given by → E = 200 cos[(0. 5 × 103 m−1)x −(1. 5 × 1011 rad s−1)t] V m−1 ˆj. If this wave falls normally on a perfectly reflecting surface having an area of 100 cm2 . If the radiation pressure exerted by the E.M. wave on the surface during a 10 min exposure is k N m−2 . Find the value of k 109

Q28.Two wires of same length and thickness having specific resistances 6 Ω cm and 3 Ω cm respectively are connected in parallel. The effective resistivity is ρ Ωcm. The value of ρ to the nearest integer, is ___ .

Q28.A plane electromagnetic wave with a frequency of 30 MHz travels in free space. At a particular point in space and time, the electric field is 6 V m−1 . The magnetic field at this point will be x × 10−8 T. The value of x is,

Q28.An unpolarized light beam is incident on the polarizer of a polarization experiment and the intensity of light beam emerging from the analyzer is measured as 100 Lumens. Now, if the analyzer is rotated around the horizontal axis (direction of light) by 30° in clockwise direction, the intensity of emerging light will be _______Lumens.

Q28.The circuit shown in the figure consists of a charged capacitor of capacity 3 μF and a charge of 30 μC. At time t = 0, when the key is closed, the value of current flowing through the 5 MΩ resistor is x μA. The value of x to the nearest integer is

Q28.Two identical conducting spheres with negligible volume have 2. 1 nC and −0. 1 nC charges, respectively. They are brought into contact and then separated by a distance of 0. 5 m. The electrostatic force acting between the spheres is ___ ×10−9 N . [Given : 4πε0 = 9×1091 SI unit]

Q28.A coil of inductance 2 H having negligible resistance is connected to a source of supply whose voltage is given by V = 3t volt. (where t is in second). If the voltage is applied when t = 0, then the energy stored in the coil JEE Main 2021 (25 Feb Shift 1) JEE Main Previous Year Paper after 4 s in J ,