Practice Questions

Q24.A resistor dissipates 192 J of energy in 1 s when a current of 4 A is passed through it. Now, when the current is doubled, the amount of thermal energy dissipated in 5 s is _____________ J .

Q25.A galaxy is moving away from the earth at a speed of 286 km s−1 . The shift in the wavelength of a red line at 630 nm is x × 10−10 m. The value of x, to the nearest integer, is ___ . [Take the value of the speed of the light c, as 3 × 108 m s−1 ]

Q25.A tuning fork is vibrating at 250 Hz. The length of the shortest closed organ pipe that will resonate with the tuning fork will be _____ cm. (Take speed of sound in air as 340 m s−1 )

Q25.Two travelling waves produces a standing wave represented by equation. y = (1. 0 mm) cos[(1. 57 cm−1)x] sin[(78. 5 s−1) t]. The node closest to the origin in the region x > 0 will be at x =. . . . . . (in cm).

Q25.The percentage increase in the speed of transverse waves produced in a stretched string if the tension is increased by 4% , will be ___ % .

Q25.A common transistor radio set requires 12 V D . C . for its operation. The D . C . source is constructed by using a transformer and a rectifier circuit, which are operated at 220 V A . C . on standard domestic A . C . supply. The number of turns of secondary coil are 24, then the number of turns of primary are

Q26.A series LCR circuit of R = 5 Ω, L = 20 mH and C = 0. 5 μF is connected across an AC supply of 250 V , having variable frequency. The power dissipated at resonance condition is ________ ×102 W.

Q26.At very high frequencies, the effective impedance of the given circuit will be _________Ω .

Q26.The amplitude of wave disturbance propagating in the positive x-direction is given by y = 1 at time t = 0 (1+x)2 and y = 1 at t = 1 s, where x and y are in metres. The shape of wave does not change during the 1+(x−2)2 propagation. The velocity of the wave will be m s−1.

Q26.In an electrical circuit, a battery is connected to pass 20 C of charge through it in a certain given time. The potential difference between two plates of the battery is maintained at 15 V . The workdone by the battery is _______ J

Q26.For an ideal heat engine, the temperature of the source is 127°C. In order to have 60% efficiency the temperature of the sink should be __________ ∘C. (Round off to the nearest integer)

Q26.A uniform heating wire of resistance 36 Ω is connected across a potential difference of 240 V . The wire is then cut into half and a potential difference of 240 V is applied across each half separately. The ratio of power dissipation in first case to the total power dissipation in the second case would be 1: 𝑥, where 𝑥 is -1

Q26.The electric field in a region is given by E = 5 E0ˆi + 5 E0ˆj field through a rectangular surface, area 0. 4 m2 parallel to the Y −Z plane is _______ N m2 C−1 .

Q27.A fringe width of 6 mm was produced for two slits separated by 1 mm apart. The screen is placed 10 m away. The wavelength of light used is x nm. The value of x to the nearest integer is ______.

Q27.In Bohr's atomic model, the electron is assumed to revolve in a circular orbit of radius 0. 5 A. If the speed of electron is 2. 2 × 106 m s−1. Then the current associated with the electron will be__________ ×10−2 mA. [Take π as 22 7 ]

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 radioactive substance decays to ( 161 )th of its initial activity in 80 days. The half life of the radioactive substance expressed in days is ________.

Q28.A series LCR circuit is designed to resonate at an angular frequency ω0 = 105 rad s−1. The circuit draws 16 W power from 120 V source at resonance. The value of resistance R in the circuit is ________ Ω.

Q28.The alternating current is given by, i = {√42 sin( 2πT t) 10} __________ A.

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,

Q29. X different wavelength may be observed in the spectrum from a hydrogen sample if the atoms are excited to states with principal quantum number n = 6? The value of X is

Q29.A bandwidth of 6 MHz is available for 𝐴. 𝑀. transmission. If the maximum audio signal frequency used for modulating the carrier wave is not to exceed 6 kHz . The number of stations that can be broadcasted within this band simultaneously without interfering with each other will be __________. JEE Main 2021 (31 Aug Shift 2) JEE Main Previous Year Paper

Q29.The energy dissipated by a resistor is 10 mJ in 1 s, when an electric current of 2 mA flows through it. The resistance is ________ Ω. (Round off to the Nearest Integer)

Q30.An amplitude-modulated wave is represented by, Cm(t) = 10(1 + 0. 2 cos 12560t) sin(111 × 104t) V. The modulating frequency in kHz will be JEE Main 2021 (26 Aug Shift 1) JEE Main Previous Year Paper

Q30.A transmitting antenna has a height of 320 m and that of receiving antenna is 2000 m. The maximum distance between them for satisfactory communication in line of sight mode is d. The value of d is ________ km. = nRT is: