1. as part of their training, air force pilots make two practice landings with instruc- tars, and are rated on performance. the instructors discuss the ratings with the pilots after each landing. statistical analysis shows that pilots who make poor land ings the first time tend to do better the second time. conversely, pilots who make good landings the first time tend to do worse the second time. the conclusion: crit icism the pilots while praise makes them do worse. as a result, instructors were ordered to criticize all landings, good or bad. was this warranted by the facts? answer yes or no, and explain briefly.

Suppose you have three polarizing filters, with the second at an angle of 42∘ to the first and the third at an angle of 90∘ to the first. by what perfect will the original intensity of unpolarized light be reduced to after passing through all three filters?

Search coils and credit cards. one practical way to measure magnetic field strength uses a small, closely wound coil called a search coil. the coil is initially held with its plane perpendicular to a magnetic field. the coil is then either quickly rotated a quarter-turn about a diameter or quickly pulled out of the field. (a) derive the equation relating the total charge q that flows through a search coil to the magnetic-field magnitude b. the search coil has n turns, each with area a, and the flux through the coil is decreased from its initial maximum value to zero in a time ∆t. the resistance of the coil is r, and the total charge is q = i∆t, where i is the average current induced by the change in flux. (b) in a credit card reader, the magnetic strip on the back of a credit card is rapidly “swiped” past a coil within the reader. explain, using the same ideas that underlie the operation of a search coil, how the reader can decode the information stored in the pattern of magnetization on the strip. (c) is it necessary that the credit card be “swiped” through the reader at exactly the right speed? why or why not?

Which is the correct symbol for an isotope of iodine with 53 protons and 78 neutrons?