Which of the following is a derived unit? MCQ with Answer and Explanation

Explanation:
Leading zeros not significant. '2040' – trailing zero after decimal is significant. So digits 2,0,4,0 are significant = 4. Rule: zeros between non-zero and trailing zeros after decimal count.

Explanation:
Dispersion occurs because refractive index of glass varies with wavelength (color): n ∝ 1/λ approximately. Since v = c/n, different colors travel at different speeds in glass, causing different refraction angles (Snell's law). Frequency remains constant across media; wavelength changes. Option B is true but not the direct cause; speed difference causes angle difference. Memory tip: 'VIBGYOR: Violet bends most (slowest in glass), red least'. This conceptual question tests understanding of dispersion mechanism, crucial for optics in competitive exams. Always distinguish cause (speed variation) from property (frequency/wavelength).

Explanation:
In uniform circular motion, speed is constant but velocity direction changes continuously, requiring centripetal acceleration directed toward the center (a = v²/r). By Newton's second law, a centripetal force must act. Velocity isn't constant (direction changes); acceleration isn't zero; force is required. Memory tip: 'Uniform circular motion: constant speed, changing velocity, center-seeking acceleration'. This conceptual question tests understanding of circular dynamics, crucial for mechanics in competitive exams. Always distinguish speed (scalar) from velocity (vector) in motion analysis.