Quantum Physics.
1) In the following experiment, a photocathode of work function 2.05 eV was used.
what is the number of photons per second incident on the photocathode if the stopping potential was -0.5V, I = 0.28mA when V(voltage) = 0 and only 5% of the incident photons suceeded in ejecting photoelectron? ( this questions i duno the answer, need help.)
Probability.
Two boxes are labelled A and B. box A contain3 blue disc and 2 white disc and box B contain 2 blue and 3 white disc. A random sample of 2 disc is selected without replacement from each box. FInd the probability that at most one of the discs drawn is white ( ans = 27/100)
two friends Jane and Mary often go their shopping on sat afternoon. IF mary goes shopping , the probability that jane also goes is 0.96. If jane goes, the probability that mary goes is 0.8. The probability that neither goes is 0.07. find the probability that both go shopping.( ans = 0.72 )
Q1 physics
This one I think I totally forgot liao... can only try...
Cannot remember how the info of work function and stopping potential is related to this question...
I = 0.28mA = 0.28m C/s
1 electron contains 1.602e-19 C
so this means 1.748e15 electrons /s
thus number of photons incident per second = 1.748e15 / 0.05 = 3.5e16 photons
=> not confirmed though....
Two boxes are labelled A and B. box A contain3 blue disc and 2 white disc and box B contain 2 blue and 3 white disc. A random sample of 2 disc is selected without replacement from each box. FInd the probability that at most one of the discs drawn is white ( ans = 27/100)
P(none white) = 3/5 * 2/4 * 2/5 * 1/4 = 12/400 = 3/100
P(1 white)
= P(1 white from box A and no white from box B) + P( no white from box A and 1 white from box B)
= ( 2/5 *3/4 *2! ) * (2/5*1/4) + (3/5 * 2/4) * (3/5 * 2/4 * 2!)
= 3/50 + 9/50 = 12/50
Summing up gives 27/100
two friends Jane and Mary often go their shopping on sat afternoon. IF mary goes shopping , the probability that jane also goes is 0.96. If jane goes, the probability that mary goes is 0.8. The probability that neither goes is 0.07. find the probability that both go shopping.( ans = 0.72 )
This question english really hor.... nothing to say...
I damn tired.... no inspiration on this question yet...
P(at least one of them go)=P(J goes)+ P(M goes) - P(both J and M goes)
1-P(none go)=P(both J and M goes)/0.96+ P(both J and M goes)/0.8 - P(both J and M goes)
1-0.07=P(both J and M goes)[1/0.96+1/0.8-1]
P(both J and M goes)=0.72
I use conditional probability P(A|B)=P(A and B)/P(B)