Govt. Exams
Entrance Exams
Stars appear as point sources. Turbulent layers in the atmosphere refract starlight randomly, causing intensity variations (twinkling). Planets appear as extended sources, so refraction averaging effect minimizes visible twinkling.
# SI Units of Momentum and Impulse
Momentum and impulse are related concepts in physics, but they represent different physical quantities with distinct SI units.
Momentum is defined as the product of mass and velocity. Using the fundamental SI units of mass (kg) and velocity (m/s), we can derive momentum's unit:
Impulse is defined as the product of force and time, or equivalently, the change in momentum. Using the SI unit of force (Newton = N = kg·m/s²) and time (seconds = s):
Alternatively, since impulse equals change in momentum: \[\text{Impulse} = \Delta p = \text{kg·m/s (same as momentum)}\]
Both perspectives confirm that impulse is measured in N·s, which is equivalent to kg·m/s.
The correct answer is (C): kg·m/s and N·s — momentum is measured in kg·m/s and impulse is measured in N·s.
# Transformer Voltage Calculation
A transformer changes voltage based on the ratio of turns in its primary and secondary coils.
Step 1: Identify the Transformer Equation
For an ideal transformer, the voltage ratio equals the turns ratio between the primary and secondary coils.
Step 2: Substitute Given Values and Solve
We have: \(N_{\text{primary}} = 500\) turns, \(N_{\text{secondary}} = 100\) turns, and \(V_{\text{primary}} = 220\text{ V}\)
The secondary voltage is 44 V.
Answer: (B) 44 V
The first law of thermodynamics (ΔU = Q - W) states that energy cannot be created or destroyed, only transferred. It is based on conservation of energy.
Vertical component of velocity: u_y = 20 sin(45°) = 20/√2 = 10√2 m/s. Maximum height h = u_y²/(2g) = (10√2)²/(2×10) = 200/20 = 10 m.
Lorentz force F = q(v × B). When v is parallel to B, the cross product is zero, so no force acts
Blue light has shorter wavelength and is scattered more by atmospheric molecules (Rayleigh scattering)
Resistance R = ρL/A. When length doubles, L becomes 2L and area becomes A/2 (volume constant). New R = ρ(2L)/(A/2) = 4ρL/A = 4R
The azimuthal quantum number (l) determines the shape of the orbital (s, p, d, f)
While plant cells lack true centrosomes with centrioles, plasmodesmata serve similar intercellular communication functions. However, most plant cells lack a distinct MTOC (microtubule-organizing center).
