Physics Chapter 21

electric potential difference

the work done moving a positive test charge between two points in an electric field divided by the magnitude of the test charge

T or F: The direction of an electric field between two parallel conducting plates is *from the positive plate to the negative plate*

true

The potential increases in the direction *opposite* the electric field direction.

true

law of conservation of energy

allows you to predict the motion of objects without knowing the forces in detail

What produces an electric field?

an electric charge

Why must you use a test charge to observe an electric field?

an electric field can only be observed when it produces forces on other charges

the potential difference between 2 points does *NOT* depend on _________

magnitude of the test charge

electric field strength equation

E = F/q

volt

1 j/c

how can i detect field lines if i can't see them? (3 things)

1. place test charge at that point and determine if theres a force on it 2. divide force by test charge to find magnitude 3. to choose magnitude of test charge, pick one that's small compared to the magnitude of the charges producing the field

What charge would experience a 1.2x10^3 N force when in a uniform electric field of 4.4x10^6 N/C?

2.7x10^-10 C *process*: use formula E=F/q E= 4.4 x 10^6 N/C F= 1.2 x 10^3 N q=what you are solving for plug in numbers: (4.4x10^6)=(1.2x10^3)/q multiply q by both sides: (4.4 x10^6)q = (1.2 x 10^3) divide and get answer

It takes 1.22 J to move a charge of 3.22 C between two points in an electric field. What is the potential difference between these two points?

3.8 x 10^-1 *process*: use formula ΔV=W/q ΔV=what you are solving for W= 1.22 J q= 3.22 C plug in numbers: ΔV=1.22/3.22

Two plates of a capacitor are 12 cm apart and have an electric field of 350 N/C. What is the potential difference between the plates?

4.2 x 10^3 V *process*: use formula ΔV=Ed ΔV= what you are solving for E= 350 N/C d= 12 cm plug in numbers: ΔV=(350)(12) multiply and get answer

A negative charge of 1.4 x 10^7 C experiences a force of 1.2 N. What is the electric field magnitude at this location?

8.6 x 10^6 N/C *process*: use formula: E=F/q E=what you are solving for F= 1.2 N q= 1.4 x 10^7 C plug in numbers: E=1.2/(1.4x10^7) divide and get answer

capacitance equation

C= q/ΔV

explain the Van de Graaf generator (and be able to draw it)

It builds up a large amount of net charges in its metal dome. A belt is driven by two rollers, one attached to point A and the other is in the metal dome (B). When it's turned on, the roller builds up a negative charge and the belt builds up a positive charge. The positive ions are transported to the metal dome.

How can a Van De Graaff generator be used to show field lines?

It transfers large amounts of charge form one party of the machine to the top. If someone touches it, it is charged electrically. The charges on the person's hair repel one another and follow the field lines.

A positive test charge is located at Point A. If the test charge is moved to a Point B and then back to Point A, what is the change in electric potential?

The electric potential does not change

capacitor

a device with a specific capacitance that is used in electric circuits to store electrical energy

field lines must NEVER __________

cross

The electric potential ____ when a positive charge is moved toward a negative charge

decreases

Only ____ electric potential can be measured.

differences in

Do field lines and electric fields actually exist? How are field lines and electric fields useful?

electric fields do, but field lines do not. Field lines provide a model of an electric field but electric fields provide a method of calculating the force on a charged body.

field lines must be tangent to the direction of the _______ at any point.

field

the potential difference between two points ONLY depends on ____ and ______

field and displacement

what does the potential difference depend on?

field and displacement

what is the difference between field and force?

field does NOT depend on the test charge used to measure it, force does

the greater the line density, the ________ the magnitude of the field.

greater

The potential is *lower* near the positively charged plate.

higher

When you do positive work on a two-charge system, the electric potential energy ____

increases

Why should an electric field be measured by a small test charge?

it should be small so it does not not move the charge to a new location or change the force

what is electric potential difference is measured in?

joules per coloumb j/c (or volts)

If arrows represent electric field vectors in a picture of an electric field, how are the magnitude and the direction of the field shown?

length of the arrow: magnitude direction of the arrow: field direction

the greater the line density, the greater the ______ of the field.

magnitude

Two large, flat conducting plates parallel to each other can create a constant electric force and field. *Both are charged negatively.*

one is negative and one is positive

What do positive electric field lines look like?

pointing *away* from the center

What do negative electric field lines look like?

pointing *towards* the center

field lines always start from _________ charged objects and end on _________ charged objects.

positively ; negatively

The *electrical* difference between two points separated by a distance d in a uniform field is represented by the equation ΔV=Ed.

potential

electric potential difference ONLY depends on ________ and ________

starting and final positions on the path

the closer electric field lines are, the ________ they are

stronger

field lines must be _______ to the direction of the field at any point.

tangent

How does Coulomb's law relate to test charges?

the force exerted on a test charge in an electric field is proportional to the size of the test charge

electric field line

the lines providing a picture of the size and strength of the field around a charged object

electric potential difference does NOT depend on __________

the path used to go from one position to another

equipotential

the potential difference of zero between two or more positions in an electric field

electric field

the property of the space around a charged object that exerts a force on other charged objects

capacitance

the ratio of the net charge on one plate to the potential difference, measured in farads, between two plates of a capacitor

How can you find the electric field from two charges?

use the vector sum of the 2 charges

one j/c = one ____

volt

electric potential difference equation

ΔV= W/q

electric potential difference equation (distance)

ΔV=Ed