Who among the following has explained the phenomenon of photo-electric effect ?
- A.Max Planck
- B.Albert Einstein
- C.Neils Bohr
- D.Ernest Rutherford
Correct answer
Explanation
The correct answer is B, Albert Einstein. In 1905 Einstein explained the photoelectric effect by treating light as made of packets of energy, later called photons, and he received the 1921 Nobel Prize in Physics for this work.
In the photoelectric effect, light falling on a metal surface knocks out electrons. Einstein showed that each photon carries energy hν, and an electron escapes only if this energy is more than the metal's work function. That is why there is a threshold frequency below which no electrons come out, however bright the light. His equation: maximum kinetic energy of the electron = hν − φ.
A is wrong because Max Planck proposed in 1900 that energy is emitted in quanta to explain black-body radiation; Einstein applied the idea to light itself.
C is wrong because Niels Bohr gave the model of the hydrogen atom with fixed electron orbits.
D is wrong because Ernest Rutherford discovered the atomic nucleus through his gold-foil experiment.
Exam tip: Einstein's Nobel was for the photoelectric effect, not for relativity.
Practice Questions
View allCarborundum is used as an abrasive, because it
- A.has high thermal conductivity
- B.has low coefficient of expansion
- C.has high chemical stability
- D.is extremely hard
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Carborundum, or silicon carbide (SiC), is one of the hardest substances known, so it can grind, cut and polish other materials, which is what an abrasive must do.
Read the full explanation →Which one of the following is a major effect of long term consumption of drinking water containing little (less than 0.5 ppm) or no fluoride ?
- A.Cavity of tooth
- B.Erosion of nail
- C.Deformation of bone
- D.Mottling of tooth
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Too little fluoride in drinking water leaves tooth enamel weak, so teeth decay more easily and develop cavities, called dental caries.
Read the full explanation →Consider the following statements : 1. Potassium carbonate is a salt of a weak acid and a weak base. 2. Ammonium nitrate is a salt of a strong acid and a weak base. 3. Ammonium acetate is a salt of a weak acid and a weak base. Which of the statements given above are correct?
- A.1 and 3 only
- B.2 and 3 only
- C.1 and 2 only
- D.1, 2 and 3
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Potassium carbonate comes from a strong base and a weak acid, so statement 1 is wrong, while statements 2 and 3 are right.
Read the full explanation →Which one of the following plant hormones promotes stomatal closure during drought stress?
- A.Auxin
- B.Cytokinin
- C.Gibberellin
- D.Abscisic acid
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When water is short, leaves make more abscisic acid (ABA), which makes the guard cells lose water and close the stomata, so the plant loses less water through transpiration.
Read the full explanation →Which one of the following is considered as the basic structural element of all life forms?
- A.Phosphorus
- B.Carbon
- C.Oxygen
- D.Nitrogen
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Every biological molecule, from sugars and fats to proteins and DNA, is built on a skeleton of carbon atoms, which is why carbon is called the basic building block of life.
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