Chapter 5: Electric Fields

Question 1

What is a field?

Answer 1

A field has a value at every point in space. Examples include wind speed, temperature, light intensity, position, gravitational field, and electric field.

Question 2

What is the electric field?

Answer 2

Any charged object influences other charged objects through the electric field. The electric field at any location is the vector sum of the electric fields (influence) of all charged objects.

Question 3

Does the magnitude of the electric field get smaller or larger as you move away from a charged object?

Answer 3

The magnitude (absolute numerical value) of the electric field decreases as you move away from a charged object. The value is inversely proportional to the square of the distance from the charged object.

Question 4

Does the electric field point towards or away from a charged object?

Answer 4

It depends on the charge. The electric field points away from a positively-charged particle and towards a negatively-charged particle, so to find the direction of the electric field at any point, you must find draw a free body diagram (FBD) and find the vector sum of the field due to all charges.

Question 5

Does the electric field point towards or away from a negatively charged particle?

Answer 5

The electric field points towards a negatively charged particle.

Question 6

Does the electric field point towards or away from a positively charged particle?

Answer 6

The electric field points away from a positively charged particle.

Question 7

How does the electric field relate to the electric force? Use a description, not an equation.

Answer 7

Every charged particle has an electric field surrounding it that decreases with distance from the particle. When another charged particle interacts with the field of the first particle, it experiences an electric force as a result.

Question 8

How does the electric field relate to the electric force? Use an equation and describe the terms of the equation.

Answer 8

The force (F) between two particles is equal to the electric field (E) of one particle times the charge (q) of the second particle.

F = qE

Question 9

What is the symbol for the electric field? Is the electric field a scalar or a vector?

Answer 9

The symbol for the electric field is E. The electric field is a vector.

Question 10

What are the units of an electric field?

Answer 10

The units for an electric field are N/C (Newtons per Coulomb).

Question 11

Can an object interact with its own electric field to experience a force?

Answer 11

No. Every charged particle has an electric field, but only experiences a force by interacting with the field of a different particle.

Question 12

What does it mean for an object to have a linear charge density?

Answer 12

It means the excess charges on the object are spread out in a line, such as on a thin wire. A linear charge density (lambda) is equal to the amount of charge per meter, C/m.

Question 13

What does it mean for an object to have a surface charge density?

Answer 13

It means the excess charges on the object is spread out over a two dimensional surface, such as the surface of a table or a sphere. A surface charge density (sigma) is equal to the amount of charge per square meter, C/m^2.

Question 14

What does it mean for an object to have a volume charge density?

Answer 14

It means the excess charges on the object are spread out over a three dimensional volume, such as throughout a cube or a sphere. A surface charge density (rho) is equal to the amount of charge per cubic meter, C/m^3.

Question 15

Where will you find excess charge located on an insulator?

Answer 15

Excess charge on an insulator will be spread throughout the volume.

Question 16

Where will you find excess charge on a conductor?

Answer 16

Excess charge on a conductor will be located on the surface of the object only.

Question 17

The equation for Coulomb’s Law only applies to which kind of objects?

Answer 17

Point particles.

Question 18

You can use the Brute Force equations to find the electric field around which three kinds of extended objects?

Answer 18

A line of charge, a ring of charge, and a disk of charge.

Question 19

In the Brute Force equations for the electric field of extended objects, what does the variable y mean?

Answer 19

y is the distance from the center of the line/disk/ring to the place where the field is being calculated.

Question 20

The Brute Force equations only work if you’re measuring a field where?

Answer 20

Directly above or below the center of the line, disk, or ring.