Physics Class 12 Mini Mock - 4 - Free MCQ Practice Test with solutions,

Explanation:

• Maxwell's equations describe how electric and magnetic fields interact with each other.


• One of Maxwell's equations states that a time-varying magnetic field acts as a source of electric field.


• This means that when a magnetic field changes over time, it induces an electric field in the surrounding space.


• Similarly, another Maxwell's equation states that a time-varying electric field acts as a source of magnetic field.


• Therefore, time-varying magnetic fields and time-varying electric fields are interconnected and can generate each other.


 

Ampere's Circuital Law: 

• It gives the relationship between the current and the magnetic field created by it.
• This law says that the integral of magnetic field density (B) along an imaginary closed path is equal to the product of current enclosed by the path and permeability of the medium.

Where B = magnetic field, μ₀ = permeability of free space and I = current passing through the coil
Given:
B₁ = 0.8 T,  d₁ = 0.5 cm
The intensity of the magnetic field due to wire of infinite length at a distance d from it is given by

Where μ₀ = permeability of free space, I = current in a wire, d = distance
As current is constant in the wire, then the magnetic field varies with the distance 'd' as

B∝1 / d

⇒ B₁d₁ = B₂d₂

= 0.4 T

In vaccum, λ increases very slightly compared to that in air. As β∝ λ , therefore, width of interference fringe increases slightly.

Threshold frequency: - frequency of minimum energy required to remove electron
 
work function=3.3ev
f=3.3×1.6×10⁻¹⁹J​ /6.626×10⁻³⁴J−s
=0.8×10¹⁵Hz
=8×10¹⁴Hz

Power=IV
Where I=V_rms value of current=I_V
And V=V_rms value of voltage=E_V
Therefore, P=E_VI_V

Changes(if required):
Solution:
We can use the formula E1/E2=L1/L2
E1=2v,E2=?,l1=30,l2=60
2/E2=30/60
E2=120/30=4v

The frequency of radiation arising from the two close energy levels in hydrogen known as Lamb shift i.e. 1057 MHz is radio waves as it belongs to the short wavelength end of the electromagnetic spectrum.

Explanation:for electromagnetic induction magnet and coil both may move but relative motion between must be present

Assume the mirror is at the origin and it is moving about the origin along x direction between x = -2 and x = +2 as its extreme positions.
Assume that the object is placed at co=ordinate of x = - (2+x)
So, when mirror is at position x = -2, the object's image will be formed at x coordinate X = - 2+x 
And when the mirror is at position x = +2, the image is formed at X = 6+x 
So, the net difference in the position of image between these 2 co-ordinates is ( 6 + x  ) - ( -2 + x ) = 8
So, the amplitude will be half of this distance. So the answer is 8/2 = 4 cm. 
Option C is correct.
 

• The discovery that one particular pole of a magnet orients northward, whereas the other pole orients southward allowed people to identify the north and south poles of any magnet.
• It was then noticed that the north poles of two different magnets repel each other, and likewise for the south poles. Conversely, the north pole of one magnet attracts the south pole of other magnets.
• This situation is analogous to that of electric charge, where like charges repel and unlike charges attract. In magnets, we simply replace the charge with a pole: Like poles repel and unlike poles attract.

For point B, sin (90° – r) = _gμ_a where,
(90° – r) is critical angle.

A stationary charge produces electric field only; an uniformly moving charge produces localised electromagnetic field; an accelerated charge produces electromagnetic radiations.

we can say that any two current carrying conductors when placed near each other, will exert a magnetic force on each other.

Consider the system shown in the figure above.

Here, we have two parallel current carrying conductors, separated by a distance ‘d’, such that one of the conductors is carrying a current I₁ and the other is carrying I₂, as shown in the figure.

From the knowledge gained before, we can say that the conductor 2 experiences the same magnetic field at every point along its length due to the conductor 1.

The direction of magnetic force is indicated in the figure and is found using the right-hand thumb rule. The direction of the magnetic field, as we can see, is downwards due to the first conductor.

Rutherford declared that the "nucleus" (as he now called it) was indeed positively charged, based on the result of experiments exploring the scattering of alpha particles in various gases.

Explanation:The depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have been diffused away, or have been forced away by an electric field. The only elements left in the depletion region are ionized donor or acceptor impurities.The depletion region is so named because it is formed from a conducting region by removal of all free charge carriers, leaving none to carry a current.

K_max=eV₀=hf-hf₀
K_max=eV₀= h(f-f₀)

No force is exerted by a magnetic field on a stationary electric dipole because:

• The electric dipole consists of two equal and opposite charges.
• When stationary, the dipole does not experience any motion through the magnetic field.
• As a result, there is no induced current or change in magnetic flux.
• The magnetic field only affects moving charges or current-carrying conductors.

Therefore, the correct understanding is that a magnetic field does not exert a force on a stationary electric dipole.

Though water and ammonia are covalent molecules, they have a net dipole moment due to their distorted structure than the ideal one. Hydrochloric acid has a linear molecular structure but its net dipole moment is towards the Hydrogen atom. But methane has a symmetrical tetrahedral structure and its net dipole moment is zero hence it doesn’t behave as a permanent dipole. Methane solvents are therefore non-polar solvents.

We know that μ=(apparent depth/real depth​)

Let the thickness of the slab be t and real depth of the bubble from one side be x. Then

μ=(x/6)​=(t−x)/4​ or 1.5=x/6​ = (t−x​)/4

This gives x=9 and 1.5=(t−9)/4​ or t=15cm

Let net electric is zero at point P at a distance r from the 2mc charge.
Electric field at point P due to charge 2mc i sin direction of 8mc and its value is

Electric field at point P due to charge 8mc isin direction of 2mc and its value is

for net field to be zero

taking root on both sides

In a transistor, base bring interaction between emitter and collector. In a transistor, the base region is made very thin and lightly doped as compared to that of an emitter so that there may be less recombination of electrons and holes in this region. Due to which the base current is quite weak and the collector current is nearly equal to the emitter current.
If the base region of a transistor is doped equally to that of the emitter region, then a large electron hole recombination will take place in base, due to it, the base current would increase but collector current would decrease. Then the very purpose of a transistor would be defeated.
 

At null point (and along the axis), earth's magnetic field and bar's magnetic field are opposite in direction.
On the equatorial line, the bar's magnetic field is opposite in direction to its field on the axis. Hence, on the equatorial line, the two fields add up.
As the null points are on the axis of the bar magnet, therefore,
B1= (μ0/4π)(2M/d3)=H
On the equatorial line of magnet at same distance(d), field due to the magnet is 
B2= (μ0/4π)(M/d3)=B1/2=H/2
Therefore, total magnetic field at this point on equatorial line is 
B=B2+H=3H/2=3×0.36G/2=0.54G
 

Characteristic dimensions must be much
larger than the wavelength of light.

53 electrons in iodine atom are distributed as
2, 8, 18, 18, 7
∴ n = 5

or, x = 1.22 × 5 × 10^–3 m = 6.1 mm
∴ x is of the order of 5 mm.

Binary number system, in mathematics, positional numeral system employing 2 as the base and so requiring only two different symbols for its digits, 0 and 1, instead of the usual 10 different symbols needed in the decimal system.

Work function, φ₀ = 6.2eV.
Stopping potential V₀ = 5V.

Thus the wavelength of the incident radiation
lies in the ultraviolet region.