Electricity
Electric field strength
Fe = kq1q2 Fe = electrostatic force – N
R^2 K = electrostatic constant (8.99 x 10^9) on ref table pg 1
Q = charges – C
R = distance – m
What is the electrostatic force between two spheres possessing net charges of +2.0 C and –3.0 C, if the distance between them is 10 meters?
K=8.99 x 10^9 q1 = +2 q2 = -3 r = 10
Fe= (8.99 x 10^9) (2) (-3) Fe = -5.4 x 10 ^ -4
10
** Page 104 sample problem**
Electric field strength
E = Fe Fe = electrostatic force – N
Q Q = charges – C
E = electric field strength
What is the magnitude of electric field strength at a point in field where an electron experiences a 10 N force?
*** When electron use elementary charge – ref table pg 1– (1.60 x 10 ^ -19C)
q = (1.60 x 10 ^ -19C) 1 . = 6.25 x 10 ^ 18
Fe = 1 (1.60 x 10 ^ -19C)
What is the magnitude of the electrostatic force experienced by 1 elementary charge where the electric field strength is 5 x 10^ 3?
5 x 10 ^3 = x . Fe = 8 x 10 ^ -16
1.60 x 10 ^ -19C
*** Page 107 figure 4-2 ***
Work done, requires movement
V = w w = work – joules (j)
q. Q = charges – C
V = potential difference – volts (v)
How much energy is needed to move one electron through potential difference of 3.0 x 10 ^2 volts?
Q = 1.60 x 10 ^-19
V = 3x10^2 w= (1.60 x 10 ^-19) x (3 x 10^2)
W=? w= 4.8 x 10 ^ -17
If 8 joules of work is needed to transfer 4 C of charge, what is the potential difference?
W = 8 v= 8 v= 2
V = 4 4
I = delta q I = current - amps
T delta q =
T = time- seconds (s)
A charge of 5 C moves through a circuit in .50 s. What is the current?
I = 5 I = 10 amps
.5
What is the current in an electric circuit if 10 C is transferred in 5 s?
I= 10 I = 2 amps
5
A neutral rubber rod is rubbed with fur and acquires a charge of –5 x 10 ^ -6 C. What is the charge of the fur
Circuits
Series Circuits
Current – I (amps) measured by ammeter
I= I 1 = I 2 = I 3
Potential difference - V (volts) given off by battery, measured by voltmeter
V = V1+V2+V3
Resistance - R (ohms Ω)
Req = R1+R2+R3
** V=IR
EXAMPLE QUESTIONS
1. Given: R1 = 25 Ω, R2 = 15 Ω and total volts = 20
Can find everything using V=IR
| R1 | R2 | Total |
V | 12.5V | 7.5V | 20V |
I | .5A | .5A | .5A |
R | 25Ω | 15 Ω | 40Ω |
What is the total resistance for this circuit?
25 Ω + 15Ω = 40Ω
What is the total current for this circuit?
V=IR, 20V= (I) (40Ω), I= 20/40 = .5A
What is the potential difference for R1 and R2?
V=IR, V= (.5) (25) = 12.5V, 20-12.5=7.5, R1=12.5, R2= 7.5
2. A 100Ω resistor and an unknown resistor are connected to a 10V battery. If a potential drop across the 100Ω resistor is 4V what is the resistance of the unknown resistor?
| R1 | R2 | Total |
V | 4v | 6V | 10V |
I | .04A | .04A | .04A |
R | 100Ω | ??? Answer: 150Ω | 250Ω |
Given: R1=8Ω, R2=8 Ω, total voltage = 12V
What is the reading on the ammeter?
| R1 | R2 | total |
V | 6V | 6V | 12V |
I | .75A | .75A | ??? Answer: .75A |
R | 8Ω | 8Ω | 16Ω |
Given: R1= 40Ω, R2= 20Ω, V2= 80V
What is reading of voltmeter 1?
| R1 | R2 | Total |
V | ??? Answer: 160 | 80 | 240 |
I | 4 | 4 | 4 |
R | 40 | 20 | 60 |
Parallel Circuits
Current – I = I1 + I2 + I3 amps
Potetial difference – V=V1=V2=V3 volts
Resistance – 1/Req = 1/R1 + 1/R2 + 1/R3
V=IR
Example 1.
( ignore R3 and R4)
Known:
V=IR
30 = I (10) I= 3
Bold = known
| R1 | R2 | TOTAL |
V | 30 | 30 | 30 |
I | 3 | 2 | 5 |
R | 10 | 15 | 6 |
Waves
Waves are classified as either pulse or periodic
Types of waves
Frequency
the number of cycles or complete vibrations experienced at each point per unit
Frequency – Hertz ( Hz ) just count the number of times it hits the top
Period – the time required for one complete vibration to pass a given point
T = 1/f T=time – seconds
F – freq – Hz
Example question:
Frequency = 50 Hz. Find the period.
T = 1/f, T = 1/50 = .02s
Amplitude
Phase
Wave length
Example question:
Calculate the speed of the wave if the frequency equals 6 Hz and the wave length is 3 m. v=f l, V = 6x3, V=18
Wave fronts
Doppler effect – change in apparent frequency due to relative motion of source and observer; indirect relationship
Interference
· Nodes – points with zero displacement
· Antinodes – points with maximum displacement ( the crest and troph )
· Every elastic body has a particular frequency called its natural frequency.
Resonance
· The vibration of a body at its natural frequency because of the action of a vibrating source of the same frequency is called resonance
Diffraction
Light
Speed of light
Speed = c = 3.00 x 10 ^ 8 m/s (reference table page 1)
Law of Reflection
Light waves
Refracted ray
Reflection of light
Absolute index of refraction
V c = speed of light
V = velocity m/s
Example question:
Find the speed of light in corn oil.
C=3.00 x 10^8, n= 1.47
3.0 x 10^8= 1.47v v= 2.04 x 10^8
Refraction of light
Snell’s law
Monochromatic
Modern Physics
Quantum theory
· Electromagnetic energy is emitted from and absorbed by matter in discreet amounts or packets. Packets are called quantum. Quanta – plural
Energy of a quantum
· E=hf e = energy - joules
f = frequency - Hz
h = Planck's constant 6.63 x 10^-34 J*S (reference table page 1)
· Small energy values of quanta expressed as 1ev = 1.60 x 10^-19 (ref table page 1)
· Photon - quantum or a basic unit of electromagnetic energy. It is a mass less particle of light but it carries both energy and momentum.
Energy of a photon
· E photon = hf = hc/ l h = Planck’s constant
C = speed of light
· Energy of a photon has a indirect relationship with wavelength
· Energy of a photon has a direct relationship with frequency
Photon particle collisions
· X-ray photons have a higher frequency and energy than photons of visible light. When they strike a metal surface, electrons are ejected and electromagnetic energy of lower frequency is given off. Conservation of energy and momentum.
· Photons always travel at the speed of light
· The momentum of a photon depends on its wavelength or frequency
Particles have a wave nature
· Waves associated with the motion of particles of atomic or subatomic size
· Ex. Electrons. They can produce diffraction and interference patterns that we can observe.
Compton Effect (photoelectric effect)
· When light energy strikes the surface of certain metals, electrons are ejected creating a measurable current.
Physics part 2
This is what was told in physics class for part two of the final