# 4 questions

1. Jan 12, 2005

### 7bear

1. potential difference = voltage?
2. What's the difference between electrical energy and electrical potential energy ?
3. In light bulbs, when the resistance is increased, is it brighter?
4. When voltmeter or ammeter is equipped with the electric circuit, will the light bulb in the circuit be dimmer?

2. Jan 12, 2005

### kirovman

Voltage is the electrostatic potential. Potential difference is based on this idea, the difference in voltages, or potentials between 2 different components eg + and - leads on power supply. Potential difference here is:
$$V_+ - V_-$$

3. Jan 12, 2005

### vincentchan

1.) yes... if you are talking about electrostatic potential but not other (ie, gravity, spring...etc)
2.) electrical potential energy is the energy stored in the potential field...
electrical energy... hum... depend on how you difine... my english is not really good, but if you say a current in a wire is a kind of electrical energy, the answer should be NO..
3.) No.. I can see where is the confusion came from.. $$P = I^2 R$$ you may think that the power output shoud be proportional to the resistance. However, This assumtion is true only if you have a FIXED CURRENT. However, In your battery, power outlet...etc... current is not fixed. Instead, the voltage is fixed.... current decreases when the resistance increase.. $$I=V/R$$ so.... since we have FIXED VOLTAGE but not fixed currend... the formulas of power output by the light bulb should looks like $$P = V^2/R$$, which in fact inversely proportional to the resistance...
4.) for an IDEAL amp-meter, the answer is NO, However, Nothing is perfect... All amp-meter has an internal resistance, no matter how small it is... so, when you connected it to a light bulb, sure the light bulb will dimmer....