Preliminary research questions a. Proxima Centauri is the closest star that lies 4.3 light years away from the Earth. What is the distance from Earth to Proxima Centauri?

b. If the light emitted by Proxima Centauri takes more than four years to reach Earth, how are we able to see the star instantly when we point our telescope towards it?

c. Chinese astronomers in 185 B. C. recorded a supernova explosion. The supernova was located 9100 light years away from Earth. When did the actual explosion take place? (State the date in B. C.)

How do you know how many valence electrons an atom has?

An alarm clock has a current of 4.5 amps and a resistance of 3.2 ohms. what is the voltage in the circuit? a.1.4 volts b.0.71 volts c.14 volts d.46 volts

Cyclotrons are widely used in nuclear medicine for producing short-lived radioactive isotopes. these cyclotrons typically accelerate h- (the hydride ion, which has one proton and two electrons) to an energy of 5 mev to 20 mev. this ion has a mass very close to that of a proton because the electron mass is negligible—about 1 2000 of the proton’s mass. a typical magnetic field in such cyclotrons is 1.9 t. (a) what is the speed of a 5.0-mev h-? (b) if the h- has energy 5.0 mev and b = 1.9 t, what is the radius of this ion’s circular orbit?