In LR-circuit, the value of impedance is 50Ω and the resistance is 25 Ω. The value of power factor of the circuit is
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The image of the sun is formed on the photosensitive metal with a convex lens and the photoelectric current is I . If the lens is replaced by another similar lens of half the diameter and double the focal length, then photoelectric current will be
An X - ray tube is operated at a constant potential difference and it is required to get X - ray of wavelength not less then 0.2 nano-metres. Then the potential difference in kilo-volts is [h = 6.63 x 10−34 J-sec ; e = 1.6 x 10−19 C ; c = 3 x 108 ms−1]
The potential difference between the terminals of a cell in open circuit is 2.2 volts. With resistance of 5 ohm across the terminals of a cell, the terminal potential difference is 1.8 volt. The internal resistance of the cell is
Two wires of the same material are given. The first wire is twice as long as the second and has twice the diameter of the second. The resistance of the first will be
A particle of mass m moves with constant speed along a circular path of radius r under the action of force F. Its speed is
An electron of charge 'e' coulomb passes through a potential difference of V volts. Its energy in 'joules' will be
The energy of a photon of light with wavelength 5000Å is approximately 2.5eV. This way the energy of an X-ray photon with wavelength 1Å would be
A bar magnet is released into a copper ring which is directly below it. What about the acceleration of the magnet?
The pressure exerted by an electromegnetic wave of intensity I on a non-reflecting surface is (where c = Velocity of light)
The capacity of a condenser with two identical plates separated by a distance 'd' in air is 'C'. If the distance of separation is reduced to d/2 , the capacity is
If the distance between the plates of a parallel plate condenser is halved and the dielectric is doubled, then its capacity increases by
The value of g on the moon is 1/6th that on earth. A body weighing 60 kg on the earth, has weight on the moon
The factor not needed to calculate heat lost or gained when there is no change of state, is
A cyclist moving with a speed of 4.9 m−s⁻1 on a level road can take a sharp circular turn. The coefficient of friction between the cycle tyres and road is 0.5, then radius of the turn is
A circular disc of radius 0.2 meter is placed in a uniform magnetic field of induction in such a way that its axis makes an angle of . The magnetic flux linked with the disc is
Relative permittivity and permeability of a material are ℇr and μr , respectively . Which of the following values of these quantities are allowed for a diamagnetic material ?
Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature, then it will show
The extension in a string, obeying the Hooke's law, is x. The speed of sound in the stretched string is v. If the string is extended to 1.5 x, then speed of sound will be
The radio - isotope of this element is used in the treatment of cancer
A capillary tube (A) is dipped in water . Another identical tube (B) is dipped in a soap water solution . Which of the following shows the relative nature of the liquid columns in two tubes ?
In a nuclear reactor the excess reactivity can be controlled by using ---- rods
When two deuterium nuclei fuse together, in addition to tritium, we get a
Time period of a simple pendulum of length l is T1 and time period of a uniform rod of the same length l pivoted about one end and oscillating in a vertical plane is T2. Amplitude of oscillations in both the cases is small. Then T1/T2 is
With respect to air, critical angle in a medium for light of red colour [λ₁] is θ. Other facts remaining same, critical angle for light of yellow colour [λ₂] will be