The average power dissipation in pure inductance is
Answer :- d
Solution :- power =1/T ∫v(t)i(t)dt
In sinusoidal wave, V and I differ by 90 °
where A is a constant depending on the value of the inductance L or capacitance C of the component.
P=Aω²/2π [ ∫2π/sin(2ωt)dt]
period of sin(2ωt) is T′=π/ω
interval of integration of P is exactly two periods of sin(2ωt)
so finally :
Moseley's law states that
The frequency of characteristic X-ray spectral line is directly proportional to the square of atomic number of target element.
⇒ v ∝ Z2 i . e . √ v ∝ Z
or √ v = a (z − b)
Here a is constant of proportionality b is screening constant.
In a Wheatstone's bridge all the four arms have equal resistance R. If the resistance of the galvanometer arm is also R, the equivalent resistance of the combination as seen by the battery is
Emission of electrons in the photoelectric effect is possible, if
A sheet of aluminium is inserted in the air gap between the parallel plate capacitor, without touching any the two plates of the capacitor. The capacitance the capacitor is:
When a current is passed through water acidified with a dilute sulphuric acid, the gases formed at the platinum electrodes are
The resistance of a coil at 100oC is 4.2 Ω. If temperature coefficient of resistance of the coil material is 0.004oC-1, then its resistance at 0oC is
Answer :- c
Solution :- Emf, e = 20sin300t
Current, i = 4sin300t
Reactance, R = emf/I
R = 20/4
The internal resistance of a cell of e.m.f. 3 V is 0.1 Ω, If it is connected to a resistance of 2.9Ω then voltage across the cell will be
In short wave communication waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density 1011 per m-3?
A particle with a specific charge S is fired with a speed v towards a wall at a distance d, perpendicular to the wall. What minimum magnetic field must exist in this region for particle not hit the wall ?
The particle moves in a circular path with radius d if it is just to miss the wall
mv = Bqr
⇒ B = v ( q m ) d = v sd
When a current flows in a wire, there exists an electric field whose direction is
Answer :- a
Solution :- The current always flows in the same direction as the electric field. The electrons flow in the opposite direction, because they are negatively charged.
A generator at a utility company produces 100 A of current at 4000 V. The voltage is stepped up to 240000 V by a transformer before it is sent on a high voltage transmission line. The current in transmission line is
A step-up transformer has transformation ratio of 3:2 What is the voltage in secondary, if voltage in primary is 30 V ?
The coefficient of mutual inductance, when magnetic flux changes by 2 X 10-2 Wb and current changes by 0.01 A is
A point charge q is placed at a distance a/2 directly above the centre of a square of side a. The electric flux through the square assuming it to be one face of the cube is
Which of the following waves have the maximum wavelength?
A 2 μ F condenser is charged to 500V and then its plates are joined through of consistance. The heat produced in the resistance in joules is
If a point charge q be rotated in a circle of radius r around a charge Q, the work done will be
The electric potential at a point (x, y) in the xy-plane is given by: V=-kxy. The electric field intensity at a distance r from the origin varies as
An electric dipole of dipole moment p is placed in uniform electric field of strength E. If θ is the angle between p and E, then potential energy of the dipole becomes maximum, when θ is
In the following reaction, the energy released is
A radioactive element has a half life of 15 years. The fraction that will decay in 30 years is
The photoelectric threshold of a certain metal is 30 Å. If the radiation of 2000 Å is incident on the metal
Illusion in deserts is due to
A double convex lens made of air with both radii of curvature being 10 cm is placed in a medium of refractive index 1.5. The focal length and nature of lens is
In comparison to a half wave rectifier, the full wave rectifier gives lower
If a full wave rectifier circuit is operating from 50 Hz mains, then fundamental frequency in the ripple will be
The current gain for a transistor working as common-base amplifier is 0.96. If the emitter current is 7.2 mA, then the base current is
Solution :- Current gain of transistor is
α = ΔIC/ΔiE
Where ΔiC is change in collector current, and ΔiE is change in emitter current.
∴ ΔiB = ΔiE + ΔiC
= 7.2−6.91 = 0.29mA
When the conductivity of a semiconductor is only due to breaking of covalent bonds, the semiconductor is called
To obtain electrons as majority charge carriers in a semiconductor, the impurity mixed is
The impurity atom that should be added to the germanium to make it an n-type semiconductor, is
In Young's double slit experiment, an interference pattern is obtained on a screen by a light of wavelength 6000 Å coming from the coherent sources S1 and S2. At certain point P on the screen third dark fringe is formed. Then the path difference S1 p − S2p in microns is
The phase difference between any two points on a wavefront is
A ray of light falls on a transparent glass slab of refractive index 1.62. If the reflected ray and the refracted ray are mutually perpendicular, the angle of incidence is
In the propagation of light waves, the angle between the direction of vibration and plane of polarisation is
Sodium and copper have work functions 2.3 eV and 4.5 eV respectively. Then the ratio of the threshold wavelengths is nearest to