# Physical Science Review Outline for Exam III

## April 16, 2004

### Electricity - Cranking II and Ohm's Law  Ch. 9 pp 213-227.

Batteries in series - voltages add
AA batteries and D batteries - same voltage.  The big batteries last longer.
Current = flow rate of electric charge
Voltage = "pressure" that pushes the charge.
Current vs. voltage - Ohm's Law: Current is proportional to voltage.  Know what "proportional" means.
Qualitative experiment - motor to indicate current.  Current vs. voltage.
Quantitative experiment - ammeter to measure current.  Plot of current vs. voltage.
Current vs. number of lamps in parallel - experiment with motor.  More lamps in parallel mean more current.  Why?   People analogies.
Current vs. number of lamps in series.  More lamps in series means more resistance and less current.
Current in different parts of series circuits.  Does the current differ?  What is the experiment?
Ohm's Law formula:  I = V/R.
Power Formula: P = IV.

Circle mnemonics:

Practice problems:

1. A flashlight uses two D-cells.  What is the resistance of the lamp if 0.5 Ampere flows through the lamp? (answer: 6 Ohms)
2. What is the power of the flashlight above?  (answer: 1.5 Watts)
3. How much current flows through a toaster which consumes 1000 Watts at 120 Volt?  (answer: 8.33 Amperes).
4. What is the resistance in the above toaster?  (answer: 14.4 Ohms)
5. A lamp has a resistance of 20 Ohms.  How much current when connected to 120 Volts?  How much power?

### Reflection and Refraction Ch. 13, pp. 309-321.

Mirrors and light.  Law of reflection: Angle of incidence = angle of reflection.
Understand the normal (perpendicular to the surface)
Concave mirror and segmented mirror.  Segmented mirror approximates the concave mirror.  Law of reflection for each segment.
Refraction: light is bent towards the normal as it enters a more dense material.  Opposite when light leaves more dense material.  Remember car going off the road.
Internal reflection and total internal reflection.  Critical angle.
Focusing of light: concave mirror, convex lens.
Be able to draw light rays as they pass into and out of water tanks, lucite blocks, etc.

### Lens and Simple Telescope  Ch. 13, pp 321-325

Construction: what types of lenses and where?
Magnifying glass and curvature.  Which type makes a stronger magnifier when looking at close-up objects?  Which type makes a larger real image when casting an image on a screen?
Plot of lens-image distance vs. object distance for screen image.  Similarity to a camera
Effect of arbitrary-shaped aperture on the lens - darkens image because less light.
Light rays and convex lens - rays converge to a focus
Light rays and concave lens - rays diverge
Whole telescope - be able to draw cross-section.

### Light and Color Ch 12, pp 286-292; Ch. 15, pp 362-364

Mixing of colored lights.  Each combination of blue, green, red - include all three.
Composition of white light - diffraction grating and spectra.  White light composed of all colors
Analysis of each of the red, green, blue filters with the spectrum
Analysis of yellow, magenta, and cyan.  Each of these removes a primary color - hence they are "subtractive primaries"