1. Chapter 19-2: Pages 700-707 Physics
Resistance
Chapter 19-2: Pages
Physics

2. “Resistance IS FUTILE!!!” So sayeth the Borg!

3. Resistance
I. Resistance – the ratio of the potential difference across a conductor to the current it carries
R = ΔV → potential difference
I → current

4. Resistance Resistance is measured in ohms (Ω)  1 Ω = 1 Volt / Amp
Ohm’s law – the resistance is
constant over a wide range
of applied potential difference
ΔV / I = constant

5. Resistance *Ohm’s law does not hold true for all materials
- Materials that have a constant resistance over a wide range of potential differences are said to be ohmic.
- Materials that do not function according to ohm’s law are said to be non-ohmic
*Diodes are common non-ohmic devices

6. Resistance
- Resistance depends on length, cross-sectional area, material, and temperature
- Salt water and perspiration lower the body’s resistance.

7. Resistance
- Superconductors have no resistance below a critical temperature
- Superconductor – a material whose resistance is zero at or below some critical temperature which varies with each material

8. Homework:
P. 703 #1-5
P. 707 #1, 2, 4, 5, 7
Make it so. Engage!