SPSC PHYSICS 25 YEARS PAST PAPERS
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چار آپشن میں سے کسی ایک پر کلک کرنے سے جواب سرخ ہو جائے گا۔
- 5000
- 1000
- 800
- 4000
اس سوال کو وضاحت کے ساتھ پڑھیں
Explanation
- For flow in a circular pipe, turbulent flow occurs when the Reynolds number is above 4,000
- Reynolds number (Re) determines the type of flow:
- Re < 2000 → Laminar flow
- 2000 < Re < 4000 → Transitional flow
- Re > 4000 - 5000 → Turbulent flow
- For most practical cases, turbulence begins around Re = 5000.
ٹرانسفارمر کا اصول _____ ہے؟
- Mutual induction
- Ampere's law
- Motional e.m.f
- None of these
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Explanation
A transformer works on the principle of mutual induction, where a changing current in the primary coil induces a voltage in the secondary coil.This is based on Faraday's Law of Electromagnetic Induction, which states that a changing magnetic field produces an electromotive force (emf).
امپیر کے قانون میں ، انضمام ______ سے زیادہ ہے؟
- Surface
- Closed path
- Closed surface
- None of these
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Explanation
Ampere's law states that the line integral of the magnetic field around a closed path is proportional to the total current enclosed.Mathematically, , where the integral is taken over a closed loop (path).
جن مادوں کو سختی سے مقناطیسی بنایا جاسکتا ہے اسے _______ کہا جاتا ہے؟
- Ferromagnetic
- Ante-ferromagnetic
- Paramagnetic
- None of these
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Explanation
Ferromagnetic substances can be strongly magnetized due to the alignment of their atomic dipoles in the same direction.Common examples include iron, cobalt, and nickel.
- 45%
- 55%
- 60%
- None of these
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Explanation
Given:
Initial efficiency (η₁) = 50% = 0.5
Initial cold body temperature (T₁) = 17°C = 290 K
Initial hot body temperature (T₂) = unknown
We know that the efficiency of a Carnot engine is:
η = 1 - (T₁ / T₂)
0.5 = 1 - (290 K / T₂)
T₂ = 580 K
Now, the hot body temperature is increased by 145°C:
New hot body temperature (T₂') = 580 K + 145°C = 725 K
New efficiency (η₂) is:
η₂ = 1 - (T₁ / T₂')
= 1 - (290 K / 725 K)
≈ 0.6
New efficiency (η₂) is approximately 60%.
- 2.1 eV
- 4.0 eV
- 3.1 eV
- None of these
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Explanation
To find the work function, we need to calculate the energy of the photon (E) and the kinetic energy of the electron (KE), then use the equation:
φ = E - KE
E = hc / λ = 1240 eV nm / 4000 nm = 3.1 eV
KE = (1/2)mv^2 ≈ (1/2) × 9.11 × 10^-31 kg × (6 × 10^5 m/s)^2 ≈ 1.64 × 10^-19 J ≈ 1.024 eV
φ = 3.1 eV - 1.024 eV ≈ 2.076 eV ≈ 2.1 eV
آزادانہ طور پر گرتی لفٹ میں ایک سادہ لاکٹ کا وقت کیا ہوگا؟
- √1/2g
- ∞
- 0
- None of these
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Explanation
In a freely falling lift, both the pendulum and its support fall with the same acceleration (g), creating a weightless condition.Since there is no restoring force (no effective gravity), the pendulum does not oscillate, leading to an infinite time period.
تسلسل کے ایس آئی یونٹ کیا ہے؟
- NS
- NS⁻¹
- Kg m sec⁻¹
- None of these
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Explanation
Impulse is defined as the product of force and time (Impulse = Force × Time).The SI unit of impulse is Newton-second (NS), which is equivalent to kg·m/s (momentum unit).
زمین کی سطح سے فرار کی رفتار ______ ہے؟
- 9.1 km/sec
- 11.2 km/sec
- 1.7 km/sec
- None of these
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Explanation
Escape velocity is the minimum speed required for an object to escape Earth's gravitational field without further propulsion.On Earth, this velocity is 11.2 km/s.It calculated using the formula vₑ = √(2GM/R), where G is the gravitational constant, M is Earth's mass, and R is its radius.
کونیی رفتار ______ کے تحت محفوظ ہے؟
- Uniform force
- Central force
- Variable force
- None of these
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Explanation
Angular momentum is conserved when no external torque acts on a system.A central force (like gravitational or electrostatic force) always acts along the line joining the object and the center.It producing no torque, thus conserving angular momentum.
