The mode of heat transfer that can occur in vacuum is:
A. Conduction
B. Convection
C. Both conduction and convection
D. Radiation
Answer: Option D
Solution (By JKSSB Mock Tests)
Radiation transfers heat via electromagnetic waves and requires no medium, thus works in vacuum (e.g., solar energy reaching Earth). Conduction needs direct contact between particles; convection requires fluid movement. Vacuum lacks matter for conduction/convection. Memory tip: 'Radiation = only mode in vacuum'. This fundamental distinction is frequently tested in competitive exams. Applications include thermos flasks (minimizing all three modes) and space technology. Always recall that radiation speed is light speed, while conduction/convection are much slower.
The amount of heat required to change the state of 1 kg of a substance from solid to liquid at its melting point without any change in temperature is called:
Explanation:
The heat required to change a solid into a liquid at its melting point without a temperature rise is called the Latent Heat of Fusion. The word 'latent' means hidden, because this heat energy breaks intermolecular bonds to change the phase rather than increasing the kinetic energy (temperature) of the molecules.
Explanation:
Doppler effect: apparent change in frequency due to relative motion. Siren pitch changes as it approaches/recedes. Echo is reflection. Bending is diffraction. Fusion is nuclear reaction.
Explanation:
7.50 has three significant figures (7,5,0). Trailing zero after decimal is significant. If it were 7.5 cm, two significant figures. Precision indicated by decimal places.
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