SPSC Physics 25 years Past Papers

Q21: Colours of stars are due to their _____?

ستاروں کے رنگ ان کے _____ کی وجہ سے ہیں؟

Temperature

Size

Distance

Composition

Q22: The process in which pressure remains constant is called ______?

جس عمل میں دباؤ مستقل رہتا ہے اسے ______ کہا جاتا ہے؟

Isobaric

Isothermal

Adiabatic

None of these

Q23: Sound waves cannot be ______?

صوتی لہریں ______ نہیں ہوسکتی ہیں؟

Refracted

Polarized

Diffracted

None of these

Q24: Refractive index of materials is approximately equal to the square root of _____?

مواد کی ریفریجویٹ انڈیکس تقریبا _____ کے مربع جڑ کے برابر ہے؟

Magnetic permeability

Electrical permittivity

Electrical permittivity × Magnetic permeability

None of these

Explanation

The refractive index (n) of a material is given by: $n = sqrt{mu varepsilon}$ where μ is the magnetic permeability and ε is the electrical permittivity of the material.

This relation shows how light propagation depends on both electric and magnetic properties of the medium.

Q25: Phase difference between a node and an antinode is _____?

ایک نوڈ اور اینٹینوڈ کے درمیان مرحلے کا فرق _____ ہے؟

280°

90°

45°

None of these

Q26: A positive change moving with a constant velocity v enters a region of a uniform magnetic field pointing out the page. What is the direction of the magnetic force on the charge?

مستقل رفتار کے ساتھ چلنے والی ایک مثبت تبدیلی صفحہ کی نشاندہی کرنے والے یکساں مقناطیسی فیلڈ کے ایک خطے میں داخل ہوتی ہے۔ چارج پر مقناطیسی قوت کی سمت کیا ہے؟

To the top of the page

To the bottom of the page

Right

None of these

Explanation

The magnetic force on a moving charge is given by Lorentz force: $F = q (v \times B)$

Using the right-hand rule, point your fingers in the direction of velocity (v), curl them toward the magnetic field (out of the page), and your thumb points in the direction of force.

For a positive charge, the force is toward the top of the page.

Q27: The atomic diameter of a BCC crystal (if a is lattice parameter) is _____?

a/(4/√3)

a/4/13)

al(4/12)

None of these

Explanation

In a Body-Centered Cubic (BCC) lattice, the relation between the lattice parameter a and atomic radius r is: $4 r = \sqrt{3} a$

Since atomic diameter = 2r, solving gives: $Atomic Diameter = \frac{4 r}{2} = \frac{a}{4 / \sqrt{3}}$

Q28: If the distance between the charges doubles, the coulomb's force between the charges _____?

اگر چارجز کے درمیان فاصلہ دوگنا ہوجاتا ہے تو ، چارجز کے درمیان کولمب کی طاقت _____؟

One-fourth

Halves

Distance between the charges

None of these

Explanation

According to Coulomb’s Law, the electrostatic force $F$ is inversely proportional to the square of the distance between the charges:
$F propto frac{1}{r^2}$

If the distance doubles ( $r to 2r$ ), the force reduces to one-fourth of its original value:
$F' = frac{F}{4}$

Q29: For an electronic state s = 1, and 1 = 1, the number of possible values of total angular momentum of an electronic are _____?

2

3

4

None of these

Q30: The equation E = mc^2 indicates that energy _____?

Is fundamentally different than mass

And mass are closely related

Equals mass moving at the speed of the light square

None of these

Explanation

Einstein’s equation $E = mc^2$ shows that energy and mass are interchangeable, meaning mass can be converted into energy and vice versa.

This principle is fundamental in nuclear reactions, where small amounts of mass release large amounts of energy.