Physics: CUET Mock Test - 7 - CUET MCQ

The process in which an electron escapes from the metal surface is known as electron emission. Electrons are loosely bound to the nucleus, and therefore, a little energy push sets these electrons flying out of their respective orbits.

Concept:

A transistor:

• A transistor can be used as a switch or as an amplifier, but not as a rectifier.
• A rectifier is a device that converts alternating current (AC) to direct current (DC) by allowing current to flow in only one direction.
• A transistor can be used as an amplifier, amplifying a small signal into a larger one, or as a switch, allowing or blocking the flow of current.

Zener diode:

• A Zener diode is a type of diode that is designed to operate in the reverse breakdown region of its voltage-current characteristic curve.
• This makes it useful as a voltage regulator, maintaining a constant voltage across a load even as the input voltage varies.

NOT Gate:

• A NOT gate is not a universal gate, as it cannot be used to implement all possible Boolean functions. In contrast, NAND and NOR gates are universal gates, as they can be used to implement any Boolean function.

A photodiode:

• A photodiode is a type of semiconductor device that converts light into electrical current.
• It is not typically used as an oscillator, which is a device that generates a repetitive signal without the need for an external input signal.

From the above, it is clear that statements (B) and (D) are correct.

So, the correct answer is option (2).

The correct answer is option 4):

Concept:

Faraday's first law of electromagnetic induction:

Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced. If the conductor circuit is closed, a current is induced which is called an induced current

​Faraday's second law of electromagnetic induction:

The induced emf in a coil is equal to the rate of change of flux linked with the coil

Where dΦ = change in magnetic flux and e = induced e.m.f.

The negative sign says that it opposes the change in magnetic flux which is explained by Lenz law.

The correct answer is (A) is false, but (R) is true.

Concept:

Scalar quantity

• A scalar quantity is a physical quantity that only has magnitude.
• It has no direction.
• A scalar quantity is represented by a number only.
• For example – Energy, volume, mass, electric current, distance, speed, temperature, area.

Vector quantity

• A vector quantity is a physical quantity that has both a magnitude and a direction.
• For example – Torque, weight, acceleration, displacement, force, momentum, angular velocity.

Explanation:

• Electric current does have a direction: It flows from a point of high potential to a point of low potential. However, it is still considered a scalar quantity and not a vector quantity. Because vector quantities behave and are added together.
• The addition of vector quantities follows specific rules called vector addition.
• When two vector quantities are added, the result depends not just on their magnitudes but also on their directions.
• For instance, if you're traveling north and then east, your resulting direction is different than if you traveled east and then north.
• In contrast, the magnitude of the current at any point in a circuit is the sum of the currents through that point, regardless of their directions.
• This is the main rule for adding scalar quantities, not vectors.
• Thus, despite having a direction, electric current does not abide by the laws of vector addition and is therefore considered a scalar quantity.

This is why statements, (A) Electric current is a vector quantity is false, and (R) Electric current is a quantity having magnitude as well as direction is true.

Concept:

• Biot-Savarts Law: The law that gives the magnetic field generated by a constant electric current is Biot-savarts law.
• Let us take a current-carrying wire of current I and we need to find the magnetic field at a distance r from the wire then it is given by:
  

Where μ0= 4π × 10-7 T.m/A is the permeability of free space/vacuum, dl = small element of wire and r ̂ is the unit position vector of the point where we need to find the magnetic field.

Explanation:

From the above expression of the Biot-savart law, the magnetic field is:

• Directly proportional to the length of the wire. So statement (i) is correct.
• Directly proportional to the electric current. So statement (iii) is correct.
• Biot-savart law gives the magnetic field, not the electric field. So statement (ii) is wrong.

Energy stored in the capacitor
This is released as heat when the capacitor discharges through the metal block. The quantity of heat = mass xs p.heatx rise in temperature. 
Q = m x s x Δθ = 0.1 x 2.5 x 10² x 0.4 = 10 J
U = Q; 2 x 10⁴ C = 10; C = 5 x 10^-4 F = 500 μF

Capacitance of the small drop of radius r C₈ = 4πε₀r  and that of the big drop of radius R is C_B = 4πε₀R .  
The volume of 64 small drops, 
The ratio 

The breakdown of the potential of the capacitor is 220 V.

In order to prevent damage to a capacitor, it should be always used in a circuit where the p.d is less than its breakdown potential. The p.d difference can only be 200 V.

When a dielectric of constant K is introduced between the plates of a capacitor, the potential V reduces to V/K. Therefore K=8

When a dielectric is introduced between two charged plates of a capacitor having a charge Q and maintained at a potential difference of V, a reverse electric field is set up inside the dielectric due to dielectric polarization. This reduces the electric field in between the plates. The potential is also reduced.

Maximum potential is dependent on the charge on the plates. As the charge remains constant, the presence of the dielectric decreases the maximum potential between the plates.

Suppose V is the voltage of the supply and R is the resistance of each bulb.
Now, R_p = R/3 and current in ammeter, I = V/R_p = 3 V/R, provided all three bulbs are working properly.
If one bulb has broken down, then R_p = R/2 and I = 2V/R
Therefore, current decreases and since current through each bulb is V/R the same as before, brightness of bulbs is not affected.

60/40 = l/100-l, = R/8

so R=12

now changed position 8 is proportional to l and 12 to (100-l)

8/12 = l/100-l

l = 40ohm

Materials which obeys the ohm’s law show straight line in the V-I graph. Since silver is the only ohmic material in given options, it shows straight line curve.

The slope of the graph = I / V

In case of T₂, I/V is less. Hence, V/I (=R) is more.

Value of resistance increases with increasing temperature. 

Hence, T₂ >T

parallel currents attract from the below figure.
and similarly, in antiparallel currents repel.parallel currents attract from the below figure.
and similarly, in antiparallel currents repel.

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.

I₁=3A
I₂=8A
l=5m
r=0.1m
F=?
Force per unit length on the small conductor is given by:
f= μ_o2I₁I₂/4πr
Total force on the length of small conductor is
F=fl
F= μ_o2I₁I₂ l/4πr
F=4πx10^-7x2x3x8x5/4π x 0.1
F=2.4x10^-4N

The direction of force (motion) of a current carrying conductor in a magnetic field is given by Fleming’s left hand rule. 
It states that ‘ If we hold the thumb, fore finger and middle finger of the left hand perpendicular to each other such that the fore finger points in the direction of magnetic field, the middle finger points in the direction of current, then the thumb shows the direction of force (motion) of the conductor.
 

The correct answer is A.

The total impedance (Z) in an RLC circuit is given by:

where:

• R: Resistance,
• X_L = ωL: Inductive reactance,
• X_C = 1 / ωC​: Capacitive reactance.

The power factor (cos⁡ϕ) is given by:

Let’s keep this simple and to the point. We know that:
1.in a series circuit the same current flows through each component
2.the voltage across an ideal inductor L is 90˚ ahead of an AC current through it
3.the voltage across an ideal capacitor C is 90˚ behind an AC current through it
So putting these facts together we can conclude that given an AC series current the voltages across any L and C must have a phase difference of 180˚

In Rutherford's model we have a large massive core called the nucleus whereas, in Thomson's model we do not have. Thus the probability of backward scattering by Thomson's model is much less than that predicted by Rutherford model.

In the Geiger-Marsden experiment very small deflection of the beam was expected because positive charge and the negative electrons are distributed through the whole atom reducing electric field inside the atom.

We use the concept of conservation of energy and distance of closest approach in Rutherford's alpha scattering experiment to find the radius of the nucleus is proportional to the Mass Number. The consequence of this is that the density of the nucleus is a constant, independent of mass number for all nuclei.
 

For A nucleons
R=R_o​A^1/3 [R_o=constant]
 So, R∝A^1/3

The ratio of the volume of the atom and the volume of the nucleus is 10¹⁵
The radius of an atomic nucleus is of the order of 10⁻¹³cm or 10⁻¹⁵m or one Fermi unit.
On the other hand, the radius of an atom is of the order of 10⁻⁸cm or 10⁻¹⁰m or one angstrom unit.
Note:
The radius of the nucleus is much smaller than atomic radius.
The ratio of atomic radius to radius of nucleus is 10⁻¹⁰m /10⁻¹⁵m ​=10⁵
Volume is proportional to cube of radius.
The ratio of atomic radius to radius of nucleus is (10⁵)³=10¹⁵

Voltage across the electrodes of a cathode ray gun, V=500V
Charge of the electron=1.6x10^-19
Energy=eV
E= 1.6x10^-19 x 500
E=800 x 10^-19 J
E=8 x 10^-17 J

The kinetic energy (K.E.) of photoelectrons is calculated using the energy of the incident radiation, given by the formula:

• Incident Energy (E): E = hc/λ
• Where h = Planck's constant, c = speed of light, λ = wavelength
• For energy in electron volts (eV) and wavelength in Angstroms (Å), the formula simplifies to: E = 12400/λ Å

Given:

• Wavelength, λ = 1000 Å
• E = 12400 / 1000 Å
• Therefore, E = 12.4 eV

Since the work function is negligible, the K.E. of the photoelectrons is approximately the same as the incident energy: 12.4 eV.

• The electrons surrounding each atom in a semiconductor are part of a covalent bond. A covalent bond consists of two atoms "sharing" a single electron.
• Each atom forms 4 covalent bonds with the 4 surrounding atoms. Therefore, between each atom and its 4 surrounding atoms, 8 electrons are being shared.

There are two types of semiconductors: p-type and n-type. Therefore both holes and electrons conduct current respectively.