Punjab Physics 2019 — Solved MCQs

Question 1

Colour of light emitted by LED depends upon:

Accepted Answer

C. Type of material — The color of light emitted by an LED depends on the type of material it is made of. Each material emits light of a specific wavelength when electrons recombine with electron holes.

Question 2

At low temperature, a body emits radiations of:

Accepted Answer

B. Longer wavelength — At low temperatures, a body emits radiation according to Planck's law of black-body radiation. This law states that the wavelength of maximum intensity of emitted radiation is inversely proportional to the temperature of the body.

Question 3

The shortest wavelength in Lyman series is equal to:

Accepted Answer

A. A — The Lyman series in hydrogen spectral lines represents transitions of an electron from higher energy levels (n>1) to the first energy level (n=1). The shortest wavelength in the Lyman series corresponds to the transition from the n=2 energy level to the n=1 energy level, which emits ultraviolet radiation.

Question 4

Question is given below!

Accepted Answer

A. A — Here, X represents H because it equalizes the proton nunber and mass number.

Question 5

If the charges are doubled and the distance between them is also doubled, then Coulomb's force will be:

Accepted Answer

C. Remains same — If the charges are doubled and the distance between them is also doubled, the force will remain same.

Question 6

A rubber ball of radius 2cm has a charge of 5μc on its surface, which is uniformly distributed, the value of E at its centre is:

Accepted Answer

D. 5x10-6NC-1 — To find the electric field at the center of a uniformly charged sphere, we treat the sphere as a point charge located at its center. The electric field (E) at a distance (r) from a point charge (Q) is given by (E = \frac{k \cdot Q}{r^2}), where (k) is the Coulomb constant ((k \approx 9 	imes 10^9 , 	ext{N m}^2/	ext{C}^2)). For the given sphere, with a charge of (5 , \mu	ext{C}) and a radius of (2 , 	ext{cm}), the electric field at the center is calculated as:[ E = \frac{k \cdot Q}{r^2} = \frac{9 	imes 10^9 \cdot 5 	imes 10^{-6}}{(0.02)^2} = \frac{45 	imes 10^3}{0.0004} = 112500 , 	ext{N/C} = 1.125 	imes 10^5 , 	ext{N/C} ]

Question 7

Which one of the following relation is correct?

Accepted Answer

D. Joule=coulomb x volt — In electric circuits, work (energy) is done when a charge (coulomb) moves through a potential difference (voltage). The amount of work done (energy transferred) is equal to the product of the charge and the voltage, which is expressed as joule = coulomb x volt.

Question 8

In carbon resistors, which colour band indicates the tolerance of ±10%?

Accepted Answer

B. Silver — A white band in a carbon resistor indicates a tolerance of ±10%. This means that the actual resistance of the resistor can vary by up to 10% from the stated value.B) Silver: A silver band usually indicates a

Question 9

For an open circuit, terminal potential difference 'Vt' is:

Accepted Answer

B. Vt=emf — In an open circuit, the terminal potential difference is equal to the emf of the source since there is no current flowing and no voltage drop across any internal resistance.

Question 10

An electron travelling at 106m/s enters parallel in a magnetic field of 1 tesla, the magnetic force acting on it is:

Accepted Answer

A. Zero — Zero is correct. Since the electron is moving parallel to the magnetic field, the angle between the velocity vector and the magnetic field vector is 0, and the sine of 0 is 0. Therefore, the magnetic force acting on the electron is zero.

Question 11

When a charged particle is projected opposite to the direction of magnetic field, it experiences a force equal to:

Accepted Answer

D. Zero — When a charged particle is projected opposite to the direction of the magnetic field, the angle between the velocity vector and the magnetic field vector is 180 degrees. As mentioned earlier, in this case, the sine of 180 degrees is 0, so the magnetic force acting on the particle is zero.

Question 12

In order to increase the range of voltmeter RH is:

Accepted Answer

A. Increased — Increasing the resistance in series with the voltmeter (RH) will increase the range of the voltmeter. This is because a higher RH will allow the voltmeter to measure higher voltages without exceeding its maximum reading capability.

Question 13

Which device permits the flow of D.C?

Accepted Answer

C. Inductor — An inductor permits the flow of DC. It resists changes in current, so when DC flows through an inductor, it builds up a magnetic field that allows the current to continue flowing.

Question 14

For an ideal step up transformer:

Accepted Answer

B. Vsls>Vplp — In an ideal transformer, the ratio of the primary voltage (Vp) to the secondary voltage (Vs) is equal to the ratio of the number of turns in the primary coil (Np) to the number of turns in the secondary coil (Ns). Therefore, for a step-up transformer, where the secondary voltage is greater than the primary voltage, VsNs > VpNp.

Question 15

When a metal detector comes close to a metal then its frequency:

Accepted Answer

B. Remains same — The frequency of the metal detector remains constant when it comes close to a metal object.

Question 16

In RLC series circuit, at higher frequencies:

Accepted Answer

B. XL>XC — At higher frequencies (above the resonant frequency), the inductive reactance XL is greater than the capacitive reactance XC in an RLC series circuit. This is because the inductive reactance XL increases linearly with frequency (XL = 2πfL), while the capacitive reactance XC decreases inversely with frequency (XC = 1/(2πfC)).

Question 17

Which one belongs to trivalent group?

Accepted Answer

A. Aluminium — Aluminium is a member of the trivalent group because it commonly forms the Al3+ ion.

Punjab Physics 2019 — Solved Past Paper with Answers

More Punjab / UHS Solved Papers