 V s /V p = N s /N p  I p V p = I s V s  I p /I s = V s /V p = N s /N p  V s = (N s /N p )V p  I s = (N p /N s )I p  P = VI; I = P/V (I 2 R)= the power lost due to resistive heating

 3. A transformer has 50 turns on its primary coil and 100 turns on its secondary coil. a.) If the primary is connected to a 120-volt source, what is the voltage output of the secondary? b.) If the transformer is operated in reverse and the 120-volt input is applied to the 100-turn coil, what would be the voltage output?

 4. The 120-V alternating voltage from a wall socket feeds into the primary coil of a toy electric train transformer, which has a 800 turns. Calculate the number of turns in the secondary coil so that the output voltage from the transformer is 12-V enough to run a toy electric train safely.