Exam 1 - PHYS 152
Negative charges behave __________.
backwards
The bigger the charges, the __________ the electric force.
bigger
What is a field point? a - A charge that generates an electric field everywhere around it b - A charge that feels the effects of an electric field at its position c - A position where we want to solve for the electric field vector d - A position where the electric field vector is zero e - A position where the charge is zero
c - A position where we want to solve for the electric field vector
You are designing an electric staple gun. It is to fire a 0.005 kg staple that has received an electric charge of -1 mC. The stable begins at point A (to the left) and accelerates towards point B (to the right). What should be the voltage at points A and B? a - Points A and B at the same large positive voltage b - Point A at a large positive voltage and point B at 0 V c - Point A at 0 V and point B at a large positive voltage d - Points A and B at 0 V
c - Point A at 0 V and point B at a large positive voltage (because a negative charge needs to increase in voltage to accelerate)
A +5 C charge and a +3 C charge are repelling each other. What is true about the sizes of the forces? a - The force on the bigger charge is bigger b - The force on the bigger charge is smaller c - The force on each charge is the same d - The answer depends on the masses of the charged objects
c - The force on each charge is the same -This is based off of Newton's Third Law, which states that for every action there is an equal and opposite reaction
Source Charge
-A charge for which we want to know how it affects its surroundings -Is a source of some effect -A charge producing an electric field in its surroundings
Test Charge
-A small charge that we use to see the influence of source charge(s) in a given situation -We assume that a test charge does NOT affect its surroundings -Is a charge that we ask what it feels
Conducting Material
-Charges are free to move however they want through and around a conducting material
Roughly how much charge does a bolt of lightning have? a - 20 nC b - 20 μC c - 20 mC d - 20 C e - 20 kC
d - 20 C
You have 2 charges of the same magnitude. The one on the left is negative and the one on the right is positive. There is a field point, X, at the midpoint between the 2 charges. In what direction is the net electric field vector at the field point? a - North b - South c - East d - West e - Zero net electric field
d - West
1 coulomb is very very __________.
large
What unit of coulomb do we often use?
microcoulombs
By adding or removing electrons, an atom will gain a(n) __________.
net charge
If you can solve for E at point X in the source charge's surroundings, that tells a(n) __________ which way (and relative strength) to feel force.
positive test charge (it's as if you brought a positive test charge to the field point)
The bigger the radius, the __________ the electric force.
smaller
Insulating Material
-Charges are stuck onto or blocked by an insulating material -Charges only move through or around insulators if forcibly moved -Charges can transfer onto or off of an insulator where direct contact occurs with another object -Charges are not free to move on their own
An object has a net charge of +2. What will its new charge be if 2 electrons are removed?
+3e
Charging by Conduction
-Charging an object by allowing it to come into contact with an object that already has an electrical charge -Produces like charges
Charging by Induction
-Charging an object without direct contact between the object and a charge -Produces opposite charges
How does the force on a test charge compare when it is closer vs farther away from the source charge?
-Closer: Bigger force -Farther: Smaller force
How do you find the electric flux (without using the equation)?
-Count up the number of electric field lines that point out of or into a circle - If an electric field line points into a circle and then continues to point out of the circle, then the electric field of that line is zero
Electric Field (E)
-Helps us to find how arrangements of source charges will push test charges around -Is how much force you get for how much charge you have
What are some ways to increase the electric flux?
-Increase the magnitude of the charge (this would thus increase the electric field) -Increase the surface area -Have a perpendicular surface
Field Point
-Signified by an "X" -A position where we check the local electric field produced by source charge(s)
How do you charge a capacitor?
-Start with 2 neutral plates and attach a battery to it -Attach the positive side of a battery to one plate and it will become the positive plate -Attach the negative side of the batter to the other plate and it will become the negative plate
You have a neutral conductor surrounded by an insulator with no charge. How do you make the conductor have a charge of +2 C? What will happen to all of the charged particles after this takes place?
-Take out 2 of the negative charges from the conductor and put them into the insulator -The negative charges in the insulator do nothing -The negative charges in the conductor will spread evenly between the positive charges -Positive charges all still in the conductor will move to repel each other as much as they can while still being attracted to the negative charges
Electron Volt (eV)
-The KE increase if you let it go up by 1 V, or the EPE decrease if you let it go up 1 V -Is a unit, and can still be used for a proton or for something else (is NOT just used as a unit for electrons) -Is the number of volts that an object has changed by
Electric Flux
-The electric field lines pointing through an area -The amount of electric field going through a surface
What does it mean if an object has negative potential energy?
-The object is trapped -The object could be underground
List the 3 basic rules that electric forces follow.
-The stronger the charges, the larger the forces -The closer the charges, the larger the forces -Each charge feels the same size force but in opposite directions (if both are positive or both negative), or in the same direction (if one is positive and one is negative)
List the 4 rules for electric field lines.
-They cannot cross each other in space -Arrows go away from a positive charge and towards a negative charge -The number of lines coming out of a charge correlate to the charge's magnitude -The lines coming off of the charge must be evenly distributed
Conservation of Charge
-When opposite charges meet, they are NOT destroyed -This means that both charges are still present, but their effects cancel out
How do you deal with problems that have more than 1 source charge?
-You pair up the test charge with one of the source charges and put it into the Felec equation -Then pair up the test charge with the other source charge(s) and put it into the Felec equation -Bring together all of the information about the forces on the test charge -Add the vectors to determine the force on the test charge
A positive charge needs to __________ voltage to gain speed, and a negative charge needs to __________ voltage to gain speed.
-decrease -increase (aka a positive charge loses potential energy by losing voltage, and a negative charge loses potential energy by gaining voltage)
The electric force __________ the behavior between electrons and nuclei, and all but the largest collections of __________.
-dominates -mass
Electric field helps us to map out __________, and voltage helps us to map out __________.
-forces -EPE (electric potential energy)
A battery with __________ voltage pushes lots of charge onto the plates of a capacitor, and a battery with __________ voltage pushes not very much charge onto the plates of a capacitor.
-high -low
The __________ the voltage of a positive charge, the more potential energy it has. The __________ the voltage of a negative charge, the more potential energy it has.
-higher -lower
Everywhere around a positive charge, the electric field points __________. Everywhere around a negative charge, the electric field points __________.
-outward -inward
Outward ΦsubE is defined as __________, and inward ΦsubE is defined as __________.
-positive -negative
It is okay to ask what the force is on the __________ charge, but NOT on the __________ charge.
-test -source
Where the electric field lines are farther apart, the electric field is __________. Where the electric field lines are closer together, the electric field is __________.
-weaker -stronger
+1 C has the same ability to attract -1 C as what mass?
11.6 billion kg would attract another 11.6 billion kg
What are the units? q (charge)
C (coulomb)
What is the SI unit of electric charge?
Coulomb (C)
Is energy a scalar or vctor?
Scalar
Is voltage a scalar or vector?
Scalar
What are the units? EPE (electric potential energy)
J
What are the units? E (energy)
J (joule)
What are the units of EPE?
J (joules)
What are the units of voltage?
J/C
What are the units? V (volt)
J/C
The electronic flash attachment for a camera contains a capacitor for storing the energy used to produce the flash. In one such unit, the potential difference between the plates of an 850 μF capacitor is 280 V. 1) Determine the energy that is used to produce the flash in this unit. 2) How much charge is stored in the unit?
#1: - E = 1/2CV² - E = (1/2)(850 x 10^-6 F)(280 V)² = 33.32 J -------------------------------------------------------------- #2: - Q = CV - Q = (850 x 10^-6 F)(280 V) = Q = 0.238 C
A charge q1 = 4.0 x 10^-9 C experiences a net electrostatic force of 1.2 x 10^-6 N toward the north. 1) Find the electric field (magnitude and direction) at the location of q1. 2) If the charge q1 is replaced by a charge q2 = -1.5 x 10^-9 C, what force (magnitude and direction) will q2 experience?
#1: - E = Ftest / qtest - E = (1.2 x 10^-6 N) / (4 x 10^-9 C) = E = 300 N/C north (electric field is positive because q1 is a positive charge, so the force and electric field will be in the same direction, so since the force is to the north, the electric field is also to the north) -------------------------------------------------------------- #2: - E = Ftest / qtest - 300 N/C = Ftest / (-1.5 x 10^-9 C) = Ftest = 4.5 x 10^-7 N south (force is positive here because q2 is a negative charge, so the force and electric field will be in opposite directions, so since the electric field is to the north, the force must be to the south)
How much is a microcoulomb? A nanocoulomb?
- 1 μC = 10^-6 C - 1 nC = 10^-9 C
There is an electron at the origin of a coordinate plane that will serve as a test charge. 1) A +8.9 μC source charge is 5.4 x 10^-3 m to the right of the test charge. In what direction does the force exerted on the test charge point? 2) If the electrostatic force experienced by the test charge has a magnitude of 12.3 x 10^-20 N, what is the magnitude of the electric field around the test charge? 3) In what direction does the electric field point? 4) A -6.2 nC source charge is placed 1.2 x 10^-2 m to the right of the test charge. What is the electric force between the 2 point charges? What is the direction? 5) Find the net electric field around the test charge. 6) In what direction does the net electric field point in?
#1: - To the right (because the negative test charge is attracted to the positive source charge) -------------------------------------------------------------- #2: - E = Ftest / qtest - E = (12.3 x 10^-20 N) / (1.6 x 10^-19 C) = E = 0.769 N/C -------------------------------------------------------------- #3: - To the left (because the force and electric field point in opposite directions on a negative charge) -------------------------------------------------------------- #4: - r = (1.2 x 10^-2 m) - (5.4 x 10^-3 m) = r = 0.0066 m - |F| = (k ⋅ |q1q2|) / r² - |F| = (9 x 10^9 N⋅m²/C²)(8.9 x 10^-6 C)(6.2 x 10^-9 C) / (0.0066 m)² = |F| = 11.4 N = Direction: Towards each other (point A to the right and point D to the left) -------------------------------------------------------------- #5: - |FsubD| = (k ⋅ |q1q2|) / r² - |FsubD| = (9 x 10^9 N⋅m²/C²)(8.9 x 10^-9 C)(1.6 x 10^-19 C) / (1.2 x 10^-2 m)² - |FsubD| = -6.2 x 10^-14 N - FsubA = +5.4 x 10^-3 (given in #2) - Fnet = (12.3 x 10^-20 N) - (-6.2 x 10^-14 N) = Fnet = 6.2 d 10^-14 N to the left - E = Ftest / qtest - E = (6.2 c 10^-14 N) / (1.6 x 10^-19 C) = 387500 N/C -------------------------------------------------------------- #6: - To the right (because the force and electric field on a negative charge are in opposite directions)
A proton initially moving with a speed of 5.5 x 10^6 m/s encounters a voltage difference. 1) How does the proton's EPE change as it moves up to +100,000 V? 2) What is the proton's final speed?
#1: - ΔEPE = q(Vf - Vi) - ΔEPE = (1.6 x 10^-19 C)(100000 V) = ΔEPE = +1.6 x 10^-14 J ---------------------------------------- #2: - Wnc = (KEf - KEi) + (PEf - PEi) - Wnc = (1/2mvf² - 1/2mvi²) + q(Vf - Vi) - 0 J = [(1/2)(1.6 x 10^-27 kg)(vf)² - (1/2)(1.67 x 10^-27 kg)(5.5 x 10^6 m/s)²] + (1.6 x 10^-14 J) = vf = 3.33 x 10^6 m/s (this makes sense that the proton slows down because it increased in voltage, so it gained EPE)
A point "X" is to the left. 5 cm to the right is q1, and 10 cm to the right of q1 is q2. q1 = +4 x 10^-8 C, and q2 = -2 x 10^-8 C. 1) Find the net electric field (magnitude and direction) at the point labeled "X." 2) Waht force (magnitude and direction) would a charge q = -5 x 10^-9 C experience if placed at "X?"
#1: - ∣E1∣ = k∣q1∣ / r² - ∣E1∣ = (9 x 10^9 N⋅m²/C²)(4 x 10^-8 C) / (0.05 m)² = E1 = +144000 N/C (electric field is positive because it feels the electric field from q2 going to the right) - ∣E2∣ = k∣q1∣ / r² - ∣E2∣ = (9 x 10^9 N⋅m²/C²)(2 x 10^-8 C) / (0.15 m)² = E2 = +8000 N/C (electric field is positive because it feels the electric field from q1 going to the right) - Enet = 144000 N/C + 8000 N/C = Enet = +152000 N/C to the right -------------------------------------------------------------- #2: - E = Ftest / qtest - 152000 N/C = Ftest / (-5 x 10^-9 C) = Ftest = 7.6 x 10^-4 N to the left (force is to the left because a negative charge feels a force in the opposite direction of the electric field, and the electric field is to the right, so the force must be to the left)
A charge Q = +30 nC is placed at the origin. A charge of -60 nC is placed at coordinate (10 cm, 0). 1) Calculate the net force on the +30 nC charge. 2) Calculate the net force on the -60 nC charge. 3) Explain how you determined the directions of the forces.
#1: - ∣F∣ = k∣q1q2∣ / r² - ∣F∣ = (9 x 10^9 N⋅m²/C²)(30 x 10^-9 C)(60 x 10^-9 C) / (0.1 m)² = ∣F∣ = 0.00162 N = F = +0.00162 N -------------------------------------------------------------- #2: - ∣F∣ = 0.00162 N = F = -0.00162 N -------------------------------------------------------------- #3: - Since the charge in #1 is positive, the force will be in the same direction as the electric field. Since it feels an electric field to the right from the -60 nC charge, the force is also to the right (+) -Since the charge in #2 is negative, the force will be in the opposite direction as the electric field. Since it feels an electric field to the right from the +30 nC charge, the force is to the left (-)
I want to put a rightward electric force equal to 5 x 10^-16 N on an electron. What size and direction should the electric field be?
- Draw a picture - An electron is in the middle with an arrow to the right for the force of 5 x 10^-16 N - E is to the left (negative) because it always acts like a positive test charge (which would repel the negative electron) - E = Ftest / qtest - E = (5 x 10^-16 N) / (-1.6 x 10^-19 C) = E = 3125 N/C to the left
You float a 15 kg object with a charge of +1 μC at a height of 50 cm above the ground. This requires another charge on the ground beneath it. What is the sign and size of the charge on the ground?
- Draw a picture first - F = mg = Felec - Felec = (15 kg)(9.8 N/kg) = Felec = 147 N - I Felec I = k( Iq1q2 I / r²) - 147 N = [(9 x 10^9 N⋅m²/C²)(1 x 10^-6 C)(q2)] / (0.5 m)² = q2 = +4.08 x 10^-3 C (the charge is positive because it needs to repel the original charge in order to make that one float)
A -5 μC charge is 30 cm to the left of a +3 μC charge. Find the magnitude and direction of the force of the -5 μC charge.
- Draw a picture first - I Felec I = k( Iq1q2 I / r²) - I Felec I = [(9 x 10^9 N⋅m²/C²)(5 x 10^-6 C)(3 x 10^-6 C)] / (0.3 m)² = I Felec I = 1.5 N to the right
Two +3 μC charges exert a force of 15 N on each other. How far apart are they?
- Draw a picture first - I Felec I = k( Iq1q2 I / r²) - 15 N = [(9 x 10^9 N⋅m²/C²)(3 x 10^-6 C)(3 x 10^-6 C)] / r² = r = 0.073 m
The electric potential energy stored in the capacitor of a certain defibrillator is 73 J and the capacitance is 120 μF. What is the charge stored?
- E = Q² / 2C - 73 J = Q² / (2)(120 x 10^-6 F) = Q = 0.0132 C
Point A is +12 V and point B is 0 V. Imaging a 1 C positive charge will fall from point A to point B. What is its change in EPE?
- EPEf - EPEi = q(VsubB - VsubA) - EPEf - EPEi = q(Vf - Vi) - EPEf - EPEi = (1 C)(0 V - 12 V) = EPEf - EPEi = -12 C⋅V = EPEf - EPEi = -12 C(J/C) = EPEf - EPEi = -12 J
Determine the electrical force of attraction between 2 balloons with separate charges of +3.5 x 10^-8 C and -2.9 x 10^-8 C when separated by a distance of 0.65 N.
- Felec = (k ⋅ |q1q2|) / r² - Felec = (9 x 10^9 N⋅m²/C²)(3.5 x 10^-8 C)(2.9 x 10^-8 C) / (0.65 m)² = Felec = +2.16 x 10^-5 C
A balloon with a charge of 4.0 μC is held a distance of 0.70 m from a second balloon having the same charge. Calculate the magnitude of the repulsive force.
- Felec = (k ⋅ |q1q2|) / r² - Felec = (9 x 10^9 N⋅m²/C²)(4 x 10^-6 C)(4 x 10^-6 C) / 0.7 m)² = Felec = 0.29 C
Two spherical objects are separated by a distance that is 1.80 x 10^-3 m. The objects are initially electrically neutral and are very small compared to the distance between them. Each object acquires the same negative charge due to the addition of electrons. As a result, each object experiences an electrostatic force that has a magnitude of 4.55 x 10^-21 N. How many electrons did it take to produce the charge on one of the objects?
- Felec = (k ⋅ |q1q2|) / r² - Felec = (k ⋅ |q|²) / r² (I consolidated the equation by squaring "q" here because the charges are of the same magnitude) - 4.55 x 10^-21 N = (9 x 10^9 N⋅m²/C²)q² / (1.8 x 10^-3 m)² = q = -1.28 x 10^-18 C (charge is negative here because that's what it says in the instructions) - q = N(-e) - -1.28 10^-18 C = N(-1.6 x 10^-19 C) = N = 8 electrons
How far apart must 2 electrons be placed if the force of repulsion between them is equal in magnitude to the gravitational force on an electron on the surface of the earth?
- Fgravity = mg - mass of electron = 9.109 x 10^-31 kg - Fgravity = Felec = (9.109 x 10^-31 kg)(9.8 N/kg) = Felec = 8.93 x 10^-30 N - ∣Felec∣ = k∣q1q2∣ / r² - charge of electron = -e = -1.6 x 10^-19 C - 8.93 x 10^-30 N = (9 x 10^9 N⋅m²/C²)(1.6 x 10^-19 C)(1.6 x 10^-19 C)/r² = r = 5.08 m
Why is a sphere useful for Gauss's Law? How do you find the area of a sphere?
- It is useful because, if you have a sphere around a charge, then each field line will be perpendicular - Asphere = 4πr²
A bullet (mass 0.005 kg) is shot at Yoda with a speed 1220 m/s. Assuming Yoda's force is considered an electric field, he stops the bullet. He used the force with a charge of 1234567 C. What was the voltage he applied to use this force and prevent himself from being injured?
- KE = 1/2mv² - KE = (1/2)(0.005 kg)(1220 m/s)² = KE = 3721 m/s - Because this is a closed system, KE = PE = EPE - V = EPEtest / qtest - V = (3721 J) / (1234567 C) = V = 3.01 x 10^-3 V
A positive test charge q1 creates an electric field of magnitude E1 at a spot located at a distance r1 from the charge. The charge is replaced by another positive test charge q2, which creates a field of magnitude E2 = E1 at a distance of r2 = 2(r1). How is q2 related to q1?
- Let's make E1 = 1 - E1 = kq1 / (r1)² - E2 = kq2 / [2(r1)]² - Cancel the k's in each of the equations because they are like terms - E1 = q1 / (r1)² - E2 = q2 / [2(r1)]² - 1 = q1 / (r1)² (E1 equation with E1 = 1 subbed in) - 1 = q2 / [2(r1)]² (E2 equation with E1 = 1 = E2 subbed in) - q1 = r² (E1 equation) - q2 = 4r² (E2 equation) - Cancel the r's in each of the equations because they are like terms - q1 = 1 - q2 = 4 ANSWER: - q2 is 4x q1
What do each of the variables in the following equation stand for? Q = CV
- Q = charge - C = capacitance - V = voltage
A certain capacitator stores 5.3 x 10^-5 C of charge when connected to a 6.0 V battery. How much charge does it store when connected to a 9.0 V battery?
- Q1 = CV - 5.3 x 10^-5 C = C(6 V) = 8.83 x 10^-6 F - The capacitance stays constant - Q2 = CV - Q2 = (8.83 x 10^-6 F)(9 V) = Q2 = 7.95 x 10^-5 C
"Little e" (e)
- Smallest amount of charge that there can be - Stands for "elementary charge" - e = 1.6 x 1^-19 C - For electrons, this charge is negative (-e) - For protons, this charge is positive (+e)
q1 and q2 are 4.5 cm apart, and Q is inbetween them to the left, 3 cm apart from both points. q1 = 5.4 x 10^-9 C and q2 = -6.3 x 10^-9 C. Q is a point charge that was placed in the electric field of these 2 charges. What is the voltage that Q experiences?
- V = (kq1 / r1) + (kq2 / r2) - V = [(9 x 10^9 N⋅m²/C²)(5.4 x 10^-9 C) / (0.3 m)] + (9 x 10^9 N⋅m²/C²)(-6.3 x 10^-9 C) / (0.3 m)] = V = -270 V
At what distance of separation must two 1.00 μC charges be positioned in order for the repulsive force between them to be equivalent to the weight (on earth) of a 1.00 kg mass?
- W = mg - W = (1 kg)(9.8 N/kg) = W = 98 N - Felec = (k ⋅ |q1q2|) / r² - 9.8 N = (9 x 10^9 N⋅m²/C²)(10^-6 C)(10^-6 C) / r² = r = 0.03 m
During a lightning flash, there exists a potential difference of Vcloud - Vground = 1.2 x 10^9 V between a cloud and a ground. As a result, a charge of -25 C is transferred from the ground to the cloud. How much work, Wground-cloud is done on the charge by the electric force?
- Wnc = (KEf - KEi) + q(Vf - Vi) - Wnc = (0J) + (-25 C)(1.2 x 10^9 V) = Wnc = -3 x 10^10 J
You are designing an electric staple gun. It is to fire a 0.005 kg staple that has received an electric charge of -1 mC. The staple begins at point A (to the left) and accelerates towards point B (to the right) What should be the voltage difference between points A and B if you want the staple to go 1 km/s?
- WsubNC = (KEf - KEi) + (PEf - PEi) - WsubNC = (KEf - KEi) + q(Vf - Vi) - The only forces in this problem are electric forces, which are conservative, so WsubNC = 0 J - 0J = (KEf - KEi) + q(Vf - Vi) - 0J = (1/2mvf² - 0J) + q(Vf - Vi) (KEi = 0 J because the staple starts at rest) - 0 J = (1/2)(0.005 kg)(1000 m/s)² + (-0.001 C)(Vf - Vi) = Vf - Vi = 2500000 V
What is the symbol for charge?
- q (used for small charges) - Q (used for a group of charges, or for charges that are fixed / immovable)
A penny initially contains 1.76 x 10^23 protons and an equal number of electrons. The penny is then charged by removing 1.50 x 10^15 electrons. What is the final net charge on the penny?
- q = N(-e) - q = (1.5 x 10^15 electrons)(+1.6 x 10^-19 C) = qnet = +2.4 x 10^-4 C (is positive because you are subtracting the negative charge of the electrons from the originally neutral penny)
How many electrons must be removed from an electrically neutral silver dollar to give it a charge of +2.4 µC?
- q = Ne - +2.4 μC = +2.4 x 10^-6 C - +2.4 x 10^-6 C = N(1.6 x 10^-19 C) = N = 1.5 x 10^13 electrons
A magnesium nucleus contains 12 protons. Waht is the charge of a magnesium nucleus in Coulombs?
- q = Ne - q = (12 protons)(+1.6 x 10^-19 C/proton) = q = + 1.92 x 10^-18 C
What do each of the variables in the following equations mean? - q = Ne - q = N(-e)
- q = charge - N = number of extra protons or electrons - e = little e (or 1.6 x 10^-19 C)
What do each of the values represent in Coulomb's Law in the following equation? I Felec I = (1 / 4πε.)(I q1q2 I / r²) = k( Iq1q2 I / r²)
- q1 & q2: charges (C) - r: distance between the charges - ε.: epsilon naught - k = 9 x 10^9 N⋅m²/C²
What is the charge in μC of an object with 6.0 x 10^14 electrons and 4.7 x 10^14 protons?
- q1 = N(-e) - q1 = (6 x 10^14 electrons)(-1.6 x 10^-19 C) = q1 = -9.6 x 10^-5 C - q2 = Ne - q2 = (4.7 x 10^14 protons)(1.6 x 10^-19 C) = q2 = 7.52 x 10^-5 C - qnet = (-9.6 x 10^-5 C) + (7.52 x 10^-5 C) = qnet = -2.08 x 10^-5 C = qnet = -20.8 μC
A metal sphere has a charge of +7.0 µC. What is the net charge after 10 x 10^13 electrons have been placed on it?
- qnet = q1 + q2 - q2 = Ne - q2 = (10 x 10^13 electrons)(-1.6 x 10^-19 C/electron) = q2 = -1.6 x 10^-5 C - qnet = q1 + q2 - qnet = +7 x 10^-6 C - 1.6 x 10^-5 C = qnet = -9 x 10^-6 C = qnet = -9 μC
What do each of the variables in the following equation mean? ΦsubE ≡ Esub⊥ ⋅ A
- ΦsubE = electric flux - ≡ = is defined as - Esub⊥ = electric field that points perpendicular - A = area
Parallel Plate Capacitor
-2 identical conducting plates separated by a distance -One plate stores positive charge, and the other stores negative charge -So the purpose of a parallel plate capacitor is to store energy to use later
What is the value of G?
0.0000000000667 N⋅m²/kg²
What is the gravitational field around earth?
9.8 N/kg
What is the general rule (or mathematical way) to figure out a net charge when 2 charged objects collide?
Add the charges together
How do you calculate the net charge of any system?
Add up the charges from the protons and electrons
Net Electric Field
An electric field vector found by adding each E-field vector together (by adding the x and y components)
Why is there only one "q" in the electric field equation?
Because the electric field is only influenced by the source charge, NOT the test charge
What is the SI unit of capacitance?
C/V = F (coulomb/volt = farad)
You have a positively charged bar to the left and a negatively charged bar to the right. Where would you place a positive charge so that it has the most stored positive charge?
Closest to the positively charged bar
Is electricity a conservative or nonconservative force?
Conservative
Is gravity a conservative or nonconservative force?
Conservative
External Uniform Electric Field
Electric field where all of the field points have the same direction and size
Newton's Law of Universal Gravitation
Every mass attracts every other mass
What are the units? C (capacitance)
F = C/V
T or F As electric field lines move away from a point charge, they gain strength.
False
T or F A net charge of zero means that an object has no charge.
False - It means that all of the positive and negative charges cancel out
1) If Ftest is negative and qtest is negative, then E is __________. 2) If Ftest is negative and qtest is positive, then E is __________. 3) If Ftest is positive and qtest is negative, then E is __________. 4) If Ftest is positive and qtest is positive, then E is __________.
Ftest = (qtest)(E) 1) positive 2) negative 3) negative 4) positive
What are the units? Felec (electric force)
N = kg⋅m/s²
What are the units? E (electric field)
N/C
What are the units of an electric field?
N/C (newtons/coulomb)
Are atoms normally positively charged, negatively charged, or neutral?
Neutral
Net Charge
The total charge of a system of objects
Coulomb Barrier
The electrostatic barrier that doesn't allow 2 items to fuse together via a nuclear reaction
What is the new nonconservative work equation that will be helpful with electricity problems?
Wnonconservative = (KEf - KEi) + q(Vf - Vi)
What is the rule about electric field lines?
The field lines canNOT cross in space, but they can link up on charges (aka merge together)
How does an object break past the Coulomb barrier?
The object would have to move at the speed of light with a few million volts to accelerate the nuclei fast enough to fuse a pair of nuclei
What does big G represent?
The strength of gravity in the universe
T or F A net charge can be positive, negative, or zero.
True
T or F All living things are quantized.
True
T or F EPE can be either positive or negative.
True
T or F Protons and electrons are quantized.
True
T or F Voltage can be either positive or negative.
True
T or F It is hard to force nuclei together.
True (this is because of the protons in the nucleus; the protons of each nucleus want to repel each other, NOT fuse together)
What are the units? Electric Potential
V = J/C
Polarization
When the positive and negative charges go in total opposite directions of the object
The whole universe has what net charge?
Zero / Neutral
The force and electric field on a negative charge are in __________ direction as each other.
the opposite
The force and electric field on a positive charge are in __________ direction as each other.
the same
