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Describe the shape/direction of electric field lines
- They radiate outward from + charges and toward - charges (test charge is +)
- They form various shapes if they are near eachother
What does "F12" mean?
The force that 1 exerts on 2 (look at it from 2's perspective)
- tan = opp/adj
- sin = opp/hyp
- cos = adj/hyp
Other useful equations to remember regarding force?
- F=mv2/r (circular motion)
Describe electric potential of charges in a parallel plate capacitor
charges move from + to - therefore charges that are closer to the + plate have increased potential energy
How do you determine the potential energy of a group of charges? (a system)
Detrmine the potential energy (Vq = kq1q2/r) for each point and then sum them. Easy.
How do you determine the difference in energy of something between 2 plates?
- KE + PE = KE + PE
- If stopped, KE=0
- If at the - plate, PE = 0
Describe the equivalent properties (q,V,C) for a capacitor in series. A resistor? (R, I)
Describe the equivalent properties (q,V,C) for a capacitor in parallel. A resistor? (R,I)
- 1/Req = 1/R1+1/R2+1/R3
Describe Kirchoff's point rule.
The sum of current into a junction is equal to the sum of the current out of a junction
How do you perform Kirchoff's loop rule?
- 1. Choose a direction for I
- 2. Choose a start point
- 3. Move along the circuit in a direction, moving back toward point chosen in step 2
- 4. Use rules for crossing various elements and place into equation
- 5. Apply loop rule
- 6. Solve for the unknown
What is internal resistance?
The resistance WITHIN a battery (should be obvious)
Magnetic field direction?
Flows from north and into south
- eq1 = long straight wire carrying a current, causing circular magnetic field around it
- eq2 = loop carrying a current, causing straight magnetic field through center (a=radius of loop)
- eq3 = solenoid carrying a current, causing straight magnetic field through center (n = #turns/unit length)
symbols for into vs out of page (magnetic field)
x is into and o is out of
What are the various "right hand rules"
- For current in a loop: thumb aligns with current and fingers curve to show direction of B field
- For wire in a B field: I(thumb) B(index) F(middle)
- For charged particle in a B field: v(thumb) B(index) F(middle)
- ***remember if charge is negative then reverse direction!
What is the equation for the force of a circular object?
What are the two types of mechanical waves (direction)
- Transverse: the element moves vertically white the velocity is horizontal
- Longitudinal: the element AND velocity move only horizontally
What are the characteristics of a wave?
- frequency (f): # oscillations per second
- wave length (λ): distance wave travels before it repeats
- Period (t): time it takes for one cycle to be completed
Difference between electromagnetic waves and mechanical waves?
EM waves do not need a medium to travel
Wave front vs ray? What is their relationship?
- Wave front: the wave itself (the ripple after throwing a stone)
- Ray: the direction that the wave travels
- Wavefronts and rays are always perpendicular
Describe the laws of reflection, refraction, and diffraction
- *remember- all angles taken between ray and NORMAL of surface
- reflection: Angle of incidence = angle of reflection
- Law of refraction: angle of incidence > angle of refraction
- ray refracts TOWARD the normal
What is the critical angle?
- When the angle of refraction becomes 90 degrees
- Anything above is total internal reflection
Describe the reflections of a concave mirror
- a ray parallel to the principal axis is reflected through F
- a ray that pass through F is reflected parallel to the principal axis
- a ray that meets the mirror at the principal axis is reflected at the same angle
- a ray that passes through O is reflected directly back (180)
What makes an image real, inverted, larger, smaller, etc in a reflection?
- real/virtual: if the light meets in front of the mirror it is a real image
- inverted/upright: if the light meets on the opposite side of the principal axis then it is projected from it is inverted
- larger/smaller: if the light meets at a point PAST the source then it is larger
Describe the light passthrough in a converging lens
- Ray parallel to principal axis passes through focal point on other side
- Ray passing through principal axis in center of lens continues without refraction (0 change)
- Ray passing through focal point continues straight on other side
Describe light passthrough in a diverging lens
- Ray parallel to principal axis refracts away from the principal axis so that an imaginary line from the focal point is straight
- Ray passing through principal axis in center of lens continues without refraction
- Ray aimed at opposite side F (imaginary line) will come out parallel to principal axis