SST MATH PHYSICS PAST PAPER 2018
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چار آپشن میں سے کسی ایک پر کلک کرنے سے جواب سرخ ہو جائے گا۔
15
10
5
None of these
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Explanation
The turns ratio of a transformer is given by:
n = N₂ / N₁ = V₂ / V₁
Where:
- n is the turns ratio
- N₁ and N₂ are the number of turns in the primary and secondary coils
- V₁ and V₂ are the primary and secondary voltages
Given n = 5:
V₂ / V₁ = 5
This means the secondary voltage is greater than the primary voltage by a factor of 5 .
3.92 KPa
3.92 Pa
3.92 MPa
None of these
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Explanation
To find the pressure, we use the formula:
P = F / A
Where:
- P is the pressure
- F is the force (weight) = 392 N
- A is the area = 0.0001 m²
P = 392 N / 0.0001 m² = 3,920,000 Pa
To convert Pascals (Pa) to Megapascals (MPa):
3,920,000 Pa = 3.92 MPa
C² (Square of capacitance)
E° (Permittivity of free space)
E² (Square of electric intense between plates)
None of these
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Explanation
The energy density (u) in a capacitor is given by:
u = ½ε₀E²
Where:
- ε₀ is the permittivity of free space
- E is the electric field intensity between the plates
This shows that the energy density is proportional to the square of the electric field intensity (E²) .
W=τdθ
W=τd = θ
W=τ = dθ
None of these
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Explanation
The relation between work (W) done and torque (τ) in rotational motion is:
W = τdθ
Where:
- W is the work done
- τ is the torque
- dθ is the angular displacement
This shows that work done in rotational motion is the product of torque and angular displacement .
e/m = 2E/B²r
e/m = v²/B²r²
e/m = v/B²r
None of these
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Explanation
e/m = 2E/B²r²
The formula is derived by equating the magnetic Lorentz force to the centripetal force and using the kinetic energy gained from the accelerating voltage E.
This formula correctly relates the charge-to-mass ratio of an electron to the magnetic field B, radius of the circular path r, and accelerating voltage E.
Cv = 4R
Cv = 3R
Cv = 2R
None of these
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Explanation
For a polyatomic gas, Cv is typically 3R , accounting for translational and rotational degrees of freedom .
This value can increase with temperature as vibrational modes become excited , contributing to the specific heat.
di = (infinity)
di < F
di = 2F
None of these
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Explanation
When an object is placed at the principal focus (F) of a convex lens, the rays emerge parallel after refraction.
Parallel rays appear to meet at infinity , so the image is formed at infinity (very far away).
20 cm and 4 cm
30 cm and 6 cm
25 cm and 5 cm
None of these
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Explanation
Given:
Magnification M = 5
Distance between lenses L = f₀ + fₑ = 24 cm
Magnification formula M = f₀ / fₑ
Let's solve for f₀ and fₑ:
1. f₀ / fₑ = 5 => f₀ = 5fₑ
2. f₀ + fₑ = 24
Substituting f₀ = 5fₑ into the second equation:
5fₑ + fₑ = 24
6fₑ = 24
fₑ = 4 cm
Now, f₀ = 5fₑ = 5 × 4 = 20 cm
Volume of fluid
Volume flow rate
Mass of fluid
None of these
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Explanation
The equation of continuity A₁V₁ = A₂V₂ represents the conservation of mass in fluid flow.
The constant is equal to the Volume flow rate , which is the volume of fluid passing through a given area per unit time.
25m
1mm
10mm
None of these
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Explanation
If the original cable breaks at a stretch of 2 mm, each half will have half the length and thus half the maximum stretch:
Maximum stretch for half = 2 mm / 2 = 1 mm .