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HSSC physics

Written by Dr. Hamza Farooq (Physics)

PIEAS · Physics · 34 questions

Name: ____________________ Date: ____________

The dimensions of work are:
- A ML²T⁻²
- B MLT⁻²
- C ML⁻¹T⁻²
- D ML²T⁻¹
If the distance between two point charges is doubled, the force between them becomes:
- A Double
- B One quarter
- C One half
- D Four times
Capacitors of 6 μF and 3 μF are joined in series. The equivalent capacitance is:
- A 4.5 μF
- B 9 μF
- C 18 μF
- D 2 μF
The photoelectric effect supports which nature of light?
- A Particle nature
- B Magnetic nature
- C Wave nature only
- D Sound nature
The de Broglie wavelength of a particle is:
- A Independent of its momentum
- B Proportional to its momentum
- C Proportional to its mass squared
- D Inversely proportional to its momentum
The magnetic force on a charge moving parallel to a magnetic field is:
- A Zero
- B Maximum
- C Equal to qv
- D Equal to qB
If the length of a simple pendulum is made four times as large, its period becomes:
- A Twice as large
- B Half
- C Four times as large
- D One quarter
A sample of 80 g has a half-life of 5 days. How much is left after 15 days?
- A 5 g
- B 20 g
- C 40 g
- D 10 g
The power of a lens with a focal length of 0.5 m is:
- A 0.5 D
- B 1 D
- C 5 D
- D 2 D
Which of these waves is transverse?
- A Light
- B An ultrasonic wave in air
- C A compression wave in a spring
- D Sound in air
The dimensions of power are:
- A ML²T⁻²
- B ML²T⁻³
- C ML⁻²T³
- D MLT⁻³
If the mass on a spring is made four times as large, the period becomes:
- A Half
- B Four times as large
- C One quarter
- D Twice as large
At constant volume, doubling the absolute temperature of an ideal gas makes its pressure:
- A Half
- B Unchanged
- C Four times as large
- D Twice as large
The electric field at 3 m from a point charge of 2 μC is (k = 9 × 10⁹ N m²/C²):
- A 2000 N/C
- B 6000 N/C
- C 200 N/C
- D 18000 N/C
A 2 m wire carrying 4 A is placed at right angles to a field of 0.5 T. The force on it is:
- A 1 N
- B 4 N
- C 2 N
- D 16 N
A transformer has 100 turns in the primary and 400 in the secondary. A 20 V supply gives a secondary voltage of:
- A 20 V
- B 80 V
- C 2000 V
- D 5 V
The energy of a photon of frequency f is:
- A h ÷ f
- B hf²
- C f ÷ h
- D hf
An electron in an atom emits a photon when it:
- A Rises to a higher energy level
- B Stays at one level
- C Leaves the nucleus
- D Falls to a lower energy level
Binding energy per nucleon is greatest for nuclei whose mass number is close to:
- A 4
- B 238
- C 56
- D 120
After two half-lives, the fraction of the original radioactive nuclei left is:
- A 1/4
- B 0
- C 1/8
- D 1/2
In Young's double slit experiment, the fringes become wider when the wavelength of the light is:
- A Decreased
- B Unchanged
- C Increased
- D Zero
A tube closed at one end and 0.85 m long is excited at its lowest resonance (speed of sound 340 m/s). The frequency is:
- A 100 Hz
- B 200 Hz
- C 400 Hz
- D 50 Hz
According to Bernoulli's principle, in a moving fluid the pressure is lower where the speed is:
- A Zero
- B Higher
- C The same
- D Lower
If the radius of a planet is doubled and its mass stays the same, the acceleration due to gravity at its surface becomes:
- A Half
- B One quarter
- C Four times
- D Double
The angular momentum of a system is conserved when:
- A Its energy is constant
- B No force acts on it
- C Its speed is constant
- D No external torque acts on it
The kinetic energy of a 1000 kg car moving at 20 m/s is:
- A 20000 J
- B 200000 J
- C 400000 J
- D 10000 J
In a circuit with a capacitor connected to a DC source, the current in the steady state is:
- A Infinite
- B Zero
- C Maximum
- D Equal to V ÷ R
Lenz's law says that the induced current acts to:
- A Oppose the change in flux that produces it
- B Remain constant
- C Increase the change in flux
- D Stop the magnet
The rms value of an alternating voltage with a peak of 10 V is about:
- A 14.1 V
- B 7.07 V
- C 10 V
- D 5 V
An n-type semiconductor is made by doping with atoms that have:
- A Five valence electrons
- B Three valence electrons
- C Four valence electrons
- D Two valence electrons
The Carnot efficiency of an engine working between 500 K and 300 K is:
- A 40%
- B 20%
- C 80%
- D 60%
A ball is thrown vertically upward at 20 m/s (g = 10 m/s²). The time it takes to come back is:
- A 4 s
- B 10 s
- C 2 s
- D 8 s
The moment of inertia of a point mass m at distance r from the axis is:
- A m ÷ r²
- B mr
- C mr²
- D m²r
The energy stored in a spring of constant 200 N/m stretched by 0.1 m is:
- A 2 J
- B 0.1 J
- C 1 J
- D 20 J

Answer key

1. A, 2. B, 3. D, 4. A, 5. D, 6. A, 7. A, 8. D, 9. D, 10. A, 11. B, 12. D, 13. D, 14. A, 15. B, 16. B, 17. D, 18. D, 19. C, 20. A, 21. C, 22. A, 23. B, 24. B, 25. D, 26. B, 27. B, 28. A, 29. B, 30. A, 31. A, 32. A, 33. C, 34. C

Work is force times distance, so (MLT⁻²) × L = ML²T⁻².
Coulomb's law gives a force proportional to 1 ÷ r².
The value is (6 × 3) ÷ (6 + 3) = 2 μF.
Light acts as photons that eject electrons from a metal.
The wavelength is λ = h ÷ p.
The force is qvB sin θ, and sin 0 is zero.
The period is proportional to the square root of the length.
15 days is three half-lives, and 80 ÷ 8 = 10 g.
Power in dioptres is 1 ÷ f in metres.
Light waves vibrate at right angles to their direction of travel.
Power is work divided by time.
The period is proportional to the square root of the mass.
For a fixed volume the pressure is proportional to the absolute temperature.
E = kq ÷ r² = 9×10⁹ × 2×10⁻⁶ ÷ 9 = 2000 N/C.
F = BIL = 0.5 × 4 × 2 = 4 N.
The voltage is in the ratio of the turns, so 20 × 4 = 80 V.
This is Planck's relation.
The energy difference is carried away by the photon.
The curve of binding energy per nucleon peaks near iron, which has a mass number of 56.
Each half-life halves the number.
The fringe spacing is proportional to the wavelength.
The frequency is v ÷ 4L = 340 ÷ 3.4 = 100 Hz.
A faster flow has a lower pressure.
g is proportional to 1 ÷ R².
Angular momentum changes only because of a torque.
KE = ½ × 1000 × 400 = 200000 J.
Once the capacitor is charged no current flows.
It follows from the conservation of energy.
The rms value is the peak divided by √2.
Pentavalent atoms such as phosphorus give extra electrons.
Efficiency = 1 − 300 ÷ 500 = 0.4.
The time of flight is 2u ÷ g = 4 s.
This is the definition of the moment of inertia of a point mass.
E = ½kx² = ½ × 200 × 0.01 = 1 J.