Physics Questions and Answers

Neutral Equilibrium: If the body neither returns to its original position nor increases its displacement further, it will simply adopt its new position.

Examples of neutral equilibrium

• Ball moving on the ground.
• Motion of sphere.
• A roller.
• A pencil lying horizontally.
• An egg lying horizontally on a flat surface.

Comparing \( y = 10 \text{Sin} (1000\pi t - \frac{\pi x}{34}) \) with y = A sin (ωt - ϕ)

where ϕ = \(\frac{2\pi x}{λ}\)

comparing:  \(\frac{2\pi x}{λ}\) = \( \frac{\pi x}{34}\)

λ = 34 \(\times\) 2 = 68

: ϕ =  \(\frac{2\pi x}{λ}\) =  \(\frac{2\pi \times 153}{68}\)

ϕ = 4.5\(\pi\) rad = 810° or 90°

since sin 810° or 90° = 1

80 days = 4 half lives (i.e 4 x 20dqs = 80dq)

But the fraction always left by any radioactive material after 4 half lives is

\( \left ( \frac{1}{2} \right)^4 = \frac{1}{16} \)

Power of the lamp = 60W;  

\(I = {\frac{P}{V}}\)

\(I = {\frac{60}{120}}\) = \(0.5A\)

\(R = {\frac{V}{I}}\)

\(R_mains\) = \(\frac{220}{0.5}\) = \(440\Omega\)

\(R_lamp\) = \(\frac{120}{0.5}\) = \(240\Omega\)

\(\therefore\) The non-inductive resistance to keep the lamp = \((440 - 240)\Omega\)

= \(200\Omega\)

Lenz's lew of electrical magnetic induction is usefully referred to as the law of conservation of energy