a) Light caused by a transition between n=2 and n=1 levels is shown on the surface of magnesium causing emission of electron. Magnesium has a work function 3.66eV. Calculate the maximum K.E. of the emitted electrons in Joules. (5 marks)

b) When X-ray photons hit calcium, electrons are released. The frequency of a photon will have to be more than the threshold frequency of an electron is to be released. Discuss this statement in terms of the underlying physical principles. (5 marks)

c)
i) X-rays of frequency 1.53×10^(16) Hz cause the emission of electrons from a material with a maximum kinetic energy of 2.18×10^(-18)J. Calculate the threshold frequency for the release of electrons from the material. (5 marks)

ii) Describe and explain one piece of experimental evidence which shows that light is not simply a wave, but that it also has a particle nature. (5 marks)

iii) Explain why, if a photon causes an electron to jump to a higher energy level, the exact energy of the photon is critical, but if it is used to release an electron from the atom, it is the minimum energy of the photon that is critical. (5 marks)

 

 

 

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Each of you has two children, a boy and a girl, about to enter adolescence. At the present time, you are a long distance from your children and tomorrow you will be leaving on a long long journey that will prevent you from having contact with either child for the next 10 years. This is your last opportunity to inform your children of the changes that they will experience during puberty and tell them what to expect as they enter adulthood. So you want to use this chance to tell your children what you consider important to help them better deal with these changes. The only form of communication available to you is the mail. Each of you is to write ONE letter EITHER write a letter to your daughter OR a letter to your son. You must decide what to put in your letter to help your child as they deal with the changes that are coming. The choice is yours except that in the letter to your daughter you must discuss menarche, and in the letter to your son, you must discuss nocturnal emissions and spontaneous erections. You should also talk about body changes they will experience during puberty, relationships with peers, and sex. Tell them about moral development, changes in thinking, and romantic relationships. Tell them what you want them to know about sex, drinking, drug use, driving, and career exploration. You are to write your letter using vocabulary that will be understood by your children who are about 8-10 years old. Please give them a positive attitude toward the changes they will experience. You want them to have positive feelings about entering adulthood. Also, give them some good advice.

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