Punjab Physics 2022 Paper 3 — Solved MCQs

Question 1

Sec/ohm is equal to?

Accepted Answer

B. Farad — The unit of sec/ohm is equivalent to the unit of capacitance, which is the farad. This is because when you multiply resistance (ohms) by capacitance (farads), the result is time (seconds). Therefore, sec/ohm is equal to farad. In mathematical terms, this can be represented as:1sec/ohm=1Fwhere F stands for farad, the SI unit of capacitance.

Question 2

S.l unit of electric flux is?

Accepted Answer

B. Nm2/C — The SI unit of electric flux is volt-meters (V m), which is also equivalent to newton-meters squared per coulomb (N m² C⁻¹).

Question 3

If there is a single black colour band around the body of a resistor, then the value of its resistance will be:

Accepted Answer

A. Zero ohm — A resistor with a single black band is known as a zero-ohm resistor. It’s primarily used as a wire link to connect traces on a printed circuit board (PCB). The resistor package allows the same automated pick-and-place machines to place the components on a circuit board. So, the resistance value of a resistor with a single black band is 0 ohms.

Question 4

If 300 turns of wire are wound on 30 cm length , then number of turns per unit length is?

Accepted Answer

D. 1000 — The number of turns per unit length, often referred to as the turn density, can be calculated by dividing the total number of turns by the total length. In this case, you have 300 turns of wire wound on a length of 30 cm.To find the number of turns per centimeter, you would calculate:Length in cm/Number of turns​=30300​So, the number of turns per centimeter is 10 turns/cm.If you want the number of turns per meter (since 1 meter = 100 cm), you would multiply the number of turns per centimeter by 100:Turns per meter=10turns/cm×100=1000turns/meterSo, the number of turns per meter is 1000 turns/meter.

Question 5

Which of the following is not accurate potential measuring device?

Accepted Answer

A. Voltmeter — It is designed to measure the electric potential difference between two points in an electric circuit. However, the accuracy of a voltmeter can be affected by factors such as its calibration, the quality of its components, and the conditions under which it is used.

Question 6

The rod of unit length is moving at 30° through a magnetic field of IT. If the velocity of rod is 1 m/s, then induced emf in the rod will be:

Accepted Answer

C. 0.5 V — This option states that the induced emf is 0.5 V. This is the correct answer, as the calculation using the formula for induced emf results in an emf of 0.5 V.

Question 7

In alternating current circuit, inductors behave like:

Accepted Answer

C. Resistor — In AC circuits, inductors behave like resistors by resisting changes in current flow, similar to how resistors oppose the flow of current.

Question 8

Resistance of pure choke is:

Accepted Answer

C. Very small — The resistance of a pure choke, which is another term for an inductor, is very small but not zero. This small resistance is often referred to as the "AC resistance" or "winding resistance" of the inductor. This resistance arises due to the resistance of the wire used to make the inductor's coil. It is typically small because the wire used for inductor coils is chosen to have low resistance to minimize energy losses.

Question 9

The device which allows only the flow of D.C. is.

Accepted Answer

C. Inductor — An inductor allows only the flow of direct current (DC) while resisting the flow of alternating current (AC). This is because an inductor opposes changes in current, which is a characteristic of AC. In DC circuits, inductors essentially act as wires with negligible resistance.

Question 10

Curie temperature for iron is?

Accepted Answer

C. 750K — The Curie temperature for iron is approximately 770°C or 1043K. This is the temperature at which iron loses its magnetic properties. The correct option is close to this value.

Question 11

If R= 10k ohm and Rz= 100k ohm, the gain of inverting amplifier is:

Accepted Answer

B. -10 — This is the correct answer. The gain of the inverting amplifier is -10, as calculated using the formula (text{Gain} = -frac{R_{text{f}}}{R_{text{in}}}), where (R_{text{f}} = 100 text{ k}Omega ) and ( R_{text{in}} = 10 	ext{ k}Omega ).

Question 12

The open loop gain of op-amp is of the order of:

Accepted Answer

D. 105 — This is the correct answer. The open-loop gain of an op-amp is typically on the order of (105) or higher, making it a very useful component for amplifying weak signals.

Question 13

0.1 kg is equivalent to the energy of:

Accepted Answer

B. 9x1015 — Option B is correct because 0.1 kg is equivalent to 9x1015 joules of energy, based on the mass-energy equivalence principle stated by Einstein's famous equation E=mc2.

Question 14

The rest mass energy of an electron positron pair is:

Accepted Answer

B. 1.02 MeV — This option is correct because the rest mass energy of an electron is approximately 0.511 MeV and for a positron (antiparticle of the electron) is also approximately 0.511 MeV. When you add these two energies together, you get the total rest mass energy of the electron-positron pair, which is 1.022 MeV (approximately 1.02 MeV).

Question 15

First spectral series of hydrogen atom was identified by:

Accepted Answer

B. Balmer — The first spectral series of hydrogen, known as the Balmer series, was identified by Johann Balmer. He discovered a formula that described the wavelengths of the lines in this series, which are produced when electrons in hydrogen atoms transition from higher energy levels to the second energy level.

Question 16

Slow neutrons can cause fission in a:

Accepted Answer

A. Uranium 235 — Slow neutrons can cause fission in Uranium-235. Slow neutrons are more likely to be captured by Uranium-235 nuclei, leading to nuclear fission reactions.

Question 17

Radio therapy is generally done with gamma rays emitted from:

Accepted Answer

B. Cobalt 60 — Radiotherapy is often done with gamma rays emitted from Cobalt-60 sources. Cobalt-60 is a synthetic radioactive isotope with a half-life of about 5.26 years. It decays by emitting beta particles and gamma rays, and these gamma rays are used in radiotherapy to treat various medical conditions, particularly cancer.

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