Physics Class 12 Mini Mock - 3 - Free MCQ Practice Test with solutions,

The permeability of free space, μ0, is numerically equal to 4π x 10-7. For air and other non-magnetic materials, the absolute permeability is the same constant. For magnetic materials, absolute permeability is not a fixed constant but varies non-linearly with the flux density.

An oscillator is a circuit which produces a continuous, repeated, alternating waveform without any input. Oscillators basically convert unidirectional current flow from a DC source into an alternating waveform which is of the desired frequency, as decided by its circuit components.

Energy of incident light E = 12375/2000 = 6.18 eV
According to relation E = W₀ + eV₀ 

For diffraction, the width of the slit must be less than the wavelength of the incident ray.

Net force on each of the charge due to the other charges is zero. However, disturbance in any direction other than along the line on which the charges lie, will not make the charges return.

When an iron rod is inserted inside a solenoid the magnetic field inside the solenoid increases due to the high magnetic permeability of iron. Due to the increased magnetic field, the magnetic flux also increases. The self-inductance of the solenoid also increases because self-inductance (L) of the coil is directly proportional to the permeability of the material inside the solenoid. The rate of joule heating doesn’t change.

Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. It is also the measure of that magnetization. Colloquially, when a magnet is "magnetized" it has remanence.The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and is used as a source of information on the past Earth's magnetic field in paleomagnetism.The equivalent term residual magnetization is generally used in engineering applications. In transformers, electric motors and generators a large residual magnetization is not desirable (see also electrical steel) as it is an unwanted contamination, for example a magnetization remaining in an electromagnet after the current in the coil is turned off. Where it is unwanted, it can be removed by degaussing.Sometimes the term retentivity is used for remanence measured in units of magnetic flux density.

As qvB = mv²/r

Self inductance of a solenoid = 

So, self induction ∝ n²
So, inductance becomes 4 times when n is doubled.

I = 40A
r = 15 cm = 15 x 10^-2 m
∴  = 5.34 x 10^-5 T

The microfarad (symbolized µF) is a unit of capacitance, equivalent to 0.000001 (10 to the -6th power) farad. 

In the direction of electric field the electric potential decreases. This is because electric potential is the work done against the direction of the electric field.

Charges (q) = 2 × 10^-6 C,

Distance (d) = 3 cm = 3 × 10^-2 m

and electric field (E) = 2 × 10⁵ N/C. Torque (t) = q.d.

E = (2 × 10^-6) × (3 × 10^-2) × (2 × 10⁵)

= 12 × 10^-3N-m.

When the lens is in air, we have (from lens maker's equation), 1/20 = [(1.5/1) - 1) (1/R1- 1/R2). 
We are not bothered about the signs of R1 and R2 since they are unknown quantities. 
Even though we know that the convergent lens will become divergent in the denser medium, we write the lens maker's equation without bothering about the sign of its unknown focal length in the liquid. If if is the focal length in the liquid, we can write, 
1/f = ((1.5/1.6) - 1) (1/R1 - 1/R2). 
Dividing the first equation by the second, we obtain f/20 = 0.5x1.6/(-0.1) from which f = -160 cm

Dipole is defined as two equal but opposite charges, kept at a small distance and having a dipole moment. The dipole moment is simply the product of the electric charge and length of the dipole. The dielectric constant of the medium doesn’t affect the dipole moment i.e. dipole moment of an electric dipole will be the same in water as well as in the air.

More than 99.99% of the mass of any atom is concentrated in its nucleus. If the mass of protons and neutrons (which are in the nucleus of every atom) is approximately one atomic mass unit, then the relative mass of an electron is 0.0005 atomic mass units.

The visible light spectrum is the segment of the electromagnetic spectrum that the human eye can view. More simply, this range of wavelengths is called visible light. Typically, the human eye can detect wavelengths from 380 to 700 
All electromagnetic radiation is light, but we can only see a small portion of this radiation—the portion we call visible light. Cone-shaped cells in our eyes act as receivers tuned to the wavelengths in this narrow band of the spectrum. Other portions of the spectrum have wavelengths too large or too small and energetic for the biological limitations of our perception.
As the full spectrum of visible light travels through a prism, the wavelengths separate into the colors of the rainbow because each color is a different wavelength. Violet has the shortest wavelength, at around 380 nanometers, and red has the longest wavelength, at around 700 nanometers.
 

Wavelength of

where v is the velocity of the particle.
Wave length of electron

A gamma ray, or gamma radiation, is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves and so imparts the highest photon energy.

Lenz’s law is used for determining the direction of induced current.

Lenz’s law of electromagnetic induction states that the direction of induced current in a given magnetic field is such that it opposes the induced change by changing the magnetic field.

Following is the formula of Lenz’s law:

ϵ=−N (∂ϕ_B/∂t)

Where,

• ε is the induced emf

• ∂Φ_B is the change in magnetic flux

• N is the number of turns in the coil

Lenz’s law finds application in electromagnetic braking and in electric generators

• Stronger magnetic field, thicker material and low resistivity material will increase the size and effect of eddy current whereas thinner material will reduce the effect of eddy currents.

Gain or loss of charge in terms of few electrons each carrying very small charge is unobservable at macroscopic level.

The field lines of a single positive charge are radially outward.

Photo diode is used to detect light. 
In a reverse biased condition, the width of the depletion region increases as the applied reverse bias voltage increases across the diode. So, by applying a larger voltage, more of the incident photons are converted to electric current thereby increasing the efficiency.
In forward biased conditions, the width of the depletion region decreases so only a small portion of the incident photons get converted to electric current and hence the efficiency is less.
Hence photo diode in reverse biased condition detects light.

The relation between actual time and given time is:
Actual time=11:60 −given time
Actual time=11:60−3:25=8:35

A polarized dielectric is equivalent to two charged surfaces with induced charges (polarization charges). 

The focal length of the combination

∴ Power of the combinations

In reverse biasing, the positive terminal of the battery is connected to the n-type whereas the negative terminal is connected to the p-type junction. So the positive terminal tends to pull the electrons (near to the depletion layer) in n-type towards itself whereas the negative terminal pulls the holes towards itself which results in an increase in the width of the depletion layer.

Given, n = 1, B = 10^–2 T,
A = π(0.3)2m2, R = π²
f= (200/60) and ω = 2π(200/60)
Substituting these values and solving, we
get
I₀ = 6 × 10^–3 A = 6mA