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In a transformer 220 A.C. voltage is increased to 2200 volts. If the number of turns in the secondary are 2000, then the number of turns in the primary will be
In a photo electric experiment the maximum velocity of photo electons emitted
Two wires of same metal have the same length but their cross sections are in the ratio 3:1. They are joined in series. The resistance of the thicker wire is 10 Ω. The total resistance of the combination is
If elements with principal quantum number n > 4 were not allowed in nature, then, the number of possible elements would be
Correct option is B)
Hint:
Add all the elements from n=1 to n=4.
Step 1: Write the number of elements for each shell.
The number of elements for n=1 are 2.
The number of elements for n=2 are 8.
The number of elements for n=3 are 18.
The number of elements for n=4 are 32.
Step 2: adding all the elements,
from n=1 to n=4.
Total number =2+8+18+32=60
Hence option B correct
If a cell of constant electromotive force produces the same amount of heat during the same time in two independent resistances R₁ and R₂, when connected separately one after the other, across the cell, then the internal resistance of the cell is
Answer : d
Solution : Here current through the resistance R1 is I1 = ε/(r+R1)
and current through the resistance R2 is I2 = ε/(r+R2).
Also, the heat produced due to passage of current through both the resistances is same.
Hence, Q = (I1)^2R1 = (I2)^2R2
Using the values of I1 and I2 in above equation we get (ε/(r+R1))^2 R1 = (ε/(r+R2))^2 R2
where, ε is the emf and r is the internal resistance of battery.
ε^2 R1 / (r+R1)^2 = ε^2 R1 / (r+R1)^2
r^2(R1−R2) = R1R2((R1−R2)
r^2= R1R2
∴ r = (R1R2)^1/2
A wire of radius r has resistance R. If it is stretched to a radius of 3r/4, its resistance becomes
The energy required to charge a parallel plate condenser of plate separation d and plate area of crosssection A such that the uniform electric field between the plates is E, is
Energy required = 1 2 CV^{2} = 1 2 ε_{0} E^{2}Ad
Determine the current drawn from a 12 v supply with internal resistance 0.5Ω by the infinite network shown in the figure . Each resistor has Ω resistance
Let the equivalent resistance of the network be x×1
R_{s}=1+1+1+1
x = xΩ
The effective resistance x and 1Ω are in parallel
Now, the resistance R_{p},1Ω and 1Ω are in series.
For infinite resistance
applying the quadratic formula
neglecting the negative value,
Resistance of the network
Total resistance of the circuit = 2.732 + 0.5 = 3.232Ω
Current
A cell whose e.m.f. is 2V and internal resistance is 0.1Ω, is connected with a resistance of 3.9Ω. The voltage across the cell terminal will be
Answer : c
Solution : EMF of the cell(E) =2 V
internal resistance(r)= 0.1 V
External resistance(R)=3.9 V
V=IR
=(E÷(R+r))×R
=(2÷(3.9+0.1))×3.9
=1.95 V
Therefore potential difference across the terminals of the cell = 1.95V
In an electron gun, the electrons are accelerated by the potential V. If e is the charge and m is the mass of an electron, then the maximum velocity of these electrons will be
A bar magnet dropped into a coil of a conducting wire, along its axis, will fall with an acceleration
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
Given : V1=4000 volts I1=100 A V2=240000 volts
Using V1I1=V2I2
∴ 4000×100=240000×I2 ⟹I2=1.67 A
Consider the situation in the figure. The work done in taking a point charge from P to Ais W_{A}, from P to B is W_{B} and from P to C is W_{C}.
WA = WB = WC
Points A, B and C lie at the same distance from the charge q, i.e. they are lying on an equipotential surface. So, work done in moving a charge from A to B (WAB) or B toC (WBC) is zero.
Hence, work done in bringing a charge from P to A = WA,
from P to B, WB = WA+WAB = WA
and from P to C, WC = WA + WAB + WBC = WA
Hence, WA = WB = WC
A dust particle of mass 10^{3} gm is stationary between the plates of a horizontal parallel plate capacitor of 0 .016m separation which is connected to a voltage of 100V. How many fundamental charges (e = 1.6 x 10^{19} C) the dust particle carries
A capacitor of capacity C_{1} is charged upto V volt and then connected to an unchanged capacitor of capacity C_{2}. The potential difference across each capacitor will be
Charge on first capacitor = q_{1} = C_{1}_{1}
Charge on second capacitor = q_{2} = 0
When they are connected, in parallel the total charge
q = q_{1} + q_{2}
∴ q = C_{1}_{1}
and capacitance, C = C_{1} + C_{2}
Let V' be the common potential difference across each capacitaor, then q = CV'
∴ V' = q C = C1V/ C_{1} + C_{2}
A charge q is placed at the corner of a cube of side l. The electric flux passing through the cube is
Eight cubes, each side l, are required to form a Gaussian surface
So that the charge q at the corner of a small cube appears at the centre of the bigger cube
According to Gauss's law, the electric flux through the bigger cubes = q ∈ 0
Hence the electric flux through the given small cube = q 8∈ 0
Dielectric constant of a medium is unity. Its permittivity will be:

If in a photoelectric experiment, the wavelength of incident radiation is reduced from 6000Å to 4000Å, then
When a centimeter thick surface is illuminated with light of wavelength λ, stopping potential is V. When the same surface is illuminated by light of wavelength 2 λ, stopping potential is V/3. Threshold wavelength for metallic surface is
In Ramsden's eyepiece, the distance from the eye lens at which the image due to objective of focal length f is formed is
Which of the following spectrum have all the frequencies from high to low frequency range ?
While a collector emitter voltage is constant in a transistor, the collector current changes by 8.2 m A .When the emitter current changes by 8.3 m A, the value of forward current ratio h_{fe} is
When the pend of the pn junction is connected to the negative terminal of the battery and the nend to the positive terminal of the battery, then the pn junction behaves like
In a semiconductor the separation between conduction band and valence band is of the order of
When the electrical conductivity of a semiconductor is due to the breaking of its covalent bonds, then the semiconductor is said to be
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