What is the excess pressure strictly inside a soap bubble of radius R and surface tension T?
A. T / R
B. 4T / R
C. 2T / R
D. T / 2R
Answer: Option B
Solution (By JKSSB Mock Tests)
A liquid drop has only one free surface, so its excess pressure is P = 2T/R. However, a soap bubble in the air has two completely free surfaces (an inner one and an outer one). Because both surfaces exert surface tension forces inward, the total excess pressure inside a soap bubble is exactly double: P = 4T/R.
Explanation:
Frequency (f) is defined as the number of complete oscillations or cycles a wave makes in one second (measured in Hertz). The Time period (T) is the time taken to complete one full oscillation (measured in seconds). They are inversely related: T = 1/f. If a wave has a frequency of 50 Hz, its period is 1/50 seconds.
Explanation:
Work done to stretch spring from 0 to x: W₁ = ½kx². Work done from 0 to 2x: W₂ = ½k(2x)² = 2kx². Thus work for additional stretch from x to 2x: ΔW = W₂ - W₁ = 2kx² - ½kx² = ³/₂kx². Spring force is variable (F=kx), so work is integral of F·dx, yielding parabolic energy storage. Memory aid: Elastic potential energy U = ½kx²; always calculate difference for incremental work. This problem tests understanding of work done by variable forces, a common theme in energy conservation questions in competitive exams.
Explanation:
Rectifier uses diodes to convert AC to pulsating DC. Filter capacitors smooth it. Used in power supplies. Inverter does DC to AC. Transformer changes AC voltage.
No comments yet. Be the first to start the discussion!