Which two conditions must exist in order for radiation to occur?
the presence of a solid, liquid, or gas and a temperature difference
direct contact of molecules and the presence of a solid, liquid, or gas
the presence of electromagnetic waves and direct contact of molecules
a temperature difference and the presence of electromagnetic waves

In the circuit, the switch s has been open for a long time and r = 125 kohm. it is then suddenly closed. (a) determine the time constant before the switch is closed. s (b) determine the time constant after the switch is closed. _ s (c) let the switch be closed at t = 0. find the current in the switch as a function of time. (use t for time. express your answer in milliamps and seconds.) i(t) =_