Kennedy and Lilly are in science class. They are asked to prove that some forces are non-contact forces. The girls list five examples of objects exerting a force on each other without touching. Do you
agree with their list? Tell why or why not?
1. Two like magnetic poles repel each other.
2. Putting on a wool sweater can make your hair get static electricity when it rubs against the
sweater.
3. When you bring two negatively charged balloons near each other they push each other away.
4. Magnets stick to a refrigerator.
Number 1 and 3 demonstrate non-contact forces because the magnets or electrically charged objects exert
forces on each other without touching.
3 is the only example of non-contact forces since like charges repel each other.
Number 1 and 4 are non-contact forces since they both use magnets.
All four are good examples of non-contact forces since they all use either magnets or electric charge which are
non-contact forces.

The particle in a two-dimensional well is a useful model for the motion of electrons around the indole ring (3), the conjugated cycle found in the side chain of tryptophan. we may regard indole as a rectangle with sides of length 280 pm and 450 pm, with 10 electrons in the conjugated p system. as in case study 9.1, we assume that in the ground state of the molecule each quantized level is occupied by two electrons. (a) calculate the energy of an electron in the highest occupied level. (b) calculate the frequency of radiation that can induce a transition between the highest occupied and lowest unoccupied levels. 9.27 electrons around the porphine ring (4), the conjugated macrocycle that forms the structural basis of the heme group and the chlorophylls. we may treat the group as a circular ring of radius 440 pm, with 20 electrons in the conjugated system moving along the perimeter of the ring. as in exercise 9.26, assume that in the ground state of the molecule quantized each level is occupied by two electrons. (a) calculate the energy and angular momentum of an electron in the highest occupied level. (b) calculate the frequency of radiation that can induce a transition between the highest occupied and lowest unoccupied levels.

An insulated 40 ft^3 rigid tank contains air at 50 psia and 120°f. a valve connected to the tank is now opened, and air is allowed to escape until the pressure inside drops to 25 psia. the air temperature during this process is kept constant by an electric resistance heater placed in the tank. determine the electrical work done during this process.

Which of the following are used in an electrochemical cell? a. electrodes b. electrolyte c. terminals d. all of the above