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why does photoelectric emission occur only when there is a certain threshold frequency of incident radiation?

According to the particle theory of light, hf=φ+KEmax, so along with the minimum amount of energy required, there is a minimum frequency as well, φ= hf o . Thus, the incident photon must have a frequency hig...
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Answered by Nikolas P. • Physics tutor
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Calculate the pH of the solution formed when 30 cm3 of 0.150 moldm-3 aqueous sulfuric acid is added to 30 cm3 of 0.200 moldm-3 aqueous potassium hydroxide at 25 C.

H 2 SO 4 ---> 2H + + SO 4 2- KOH ---> OH - + K + Initial moles of Sulfuric acid: Volume x Concentration = Moles (30/1000) x 0.150 = 4.5x10 -3 mol Moles of H + made by sulfuric acid: It is a 1:2 ratio o...
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Answered by William D. • Chemistry tutor
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How do I answer a source analysis question?

The first thing to remember when analysing a historical primary source is that it will always be of some value. Most primary source exam questions ask of a source's value, or of its use to a historian, and i...
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Answered by Sean H. • History tutor
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How would I use the imperfect and pluperfect subjunctive in 'If Clauses'?

As A-level students, you will hear over and over again how you must have a variety of tenses - especially sophisticated ones - in your essays and your oral presentations in order to get to those top marks. O...
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Answered by Charlotte V. • Spanish tutor
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Explore Shakespeare's presentation of Jealousy in 'Othello'. You must related your discussion to relevant contextual factors and ideas from your critical reading.

Jealousy is inherent to Shakespeare's 'Othello'; with its use illuminating the disturbing traits which even the noblest of characters cannot escape. The character of 'Othello' is used by Shakespeare to exhib...
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