# Recent content by wakefreak90

1. ### Please Help Mirrors/lenses

Please Help!! Mirrors/lenses I have been working on a Physics assignment for a long time now, and I can't seem to figure out three questions. It's due tonight, so any help would be greatly appreciated!! Here they are: 1. A dentist uses a small mirror of radius 36 mm to locate a cavity in...
2. ### Transformer efficiency/primary current (help )

Transformer efficiency/primary current (help!!) Real transformers are not 100% efficient. That is, the efficiency, in percent, is represented by e = (100%) Ps/Pp. A step-down transformer has an efficiency of 92.5% is used to obtain 23.0 V from the 125 V household voltage. The current in the...
3. ### Transistor radio/kWh problem

Re: **Transistor radio/kWh problem** So if one kWh = 3.6E6 J, and the total energy is 518,400 J.. (3.6E6)/(518400) = 6.9444 --> (6.9444)(6) = 41.666 Is 41.666 cents the answer? I only have two more tries left and I don't want to get it wrong. I'm not sure if those are the correct unit...
4. ### Transistor radio/kWh problem

**Transistor radio/kWh problem** A transistor radio operates by means of a 10.0 V battery that supplies it with a 48 mA current. (a) If the cost of the battery is \$0.55 and it lasts for 300 h, what is the cost per kWh to operate the radio in this manner? 3.819 dollars/kWh...