Lecture 15 - Resistors. Circuits. Power

Lecture 15 - Resistors. Circuits. Power - ACT Switch on the...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Lecture 15 Power. Circuits. A. Equal to the time needed by the electrons in the socket to get to the lamp. ACT: Switch on the lamp When a lamp is switched on, the time it takes to light up is: Typical drift B. Zero, it’s instantaneous. C. Very short but not zero, the current is established in the wires at the speed of light. Electric fields propagate at the speed of light… speed is ~ 1 mm/s!! Power dissipation in a resistor Battery Supplied energy (tries to accelerate electrons) Resistor = - Supplied energy Dissipated energy (slows electrons down. Energy is transformed into thermal energy, light, etc) Work by the electric field when a charge d q moves across a potential difference V : supplied W Vdq  Power supplied: supplied supplied dq PV I dt  Power dissipated (in resistor): dissipated supplied PP PIV 2 2 PIR R  For Ohmic resistors Example: Resistance of a bulb Power dissipation can be bad (loss in transmission wires) or good (bulb, hair drier, etc) Example: 75-W bulb 2 2 US 120 V 192 75 W P DEMO: Current through a pickle Or for fun:
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 ACT: Traveling to Europe 22 Your hairdryer is labeled 1500 W. If you take it with you on your summer tour through Europe, where the outlets have 220 V, (and buy the adapters for the different outlet shapes), what will happen to the hairdryer? A. It will work just as in the US. B. It will be weaker. C. You’ll have to buy a new hairdryer because this one will burn down as soon as you connect it.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 7

Lecture 15 - Resistors. Circuits. Power - ACT Switch on the...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online