PHY_10_35_V2_P_E&G fields

Comparison of gravitational and electrostatic fields

10.3.1.3 - compare the characteristics of the gravitational and electrostatic fields;

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

What do these pictures describe?
By what principle are they combined in pairs?

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Group Task:
Read the text.
Compare the definition of gravitational and electric fields.
Prepare a poster and presentation for the class.
Think about what else you would like to learn from the material studied.

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Task for the 1st Pair
 
1. Read the text.
2. Highlight the similarities and differences between the gravitational and electrostatic fields.
3. Prepare a presentation for the class.
4. Prepare two false and true statements on the material studied.
 

Task for the 2nd Pair
 
1. Read the text.
2. Highlight the similarities and differences between the gravitational and electrostatic fields.
3. Prepare a presentation for the class.
4. Prepare two false and true statements on the material studied.

 
Task for the 3rd Pair
 
1. Read the text.
2. Highlight the similarities and differences between the gravitational and electrostatic fields.
3. Prepare a presentation for the class.
4. Prepare two false and true statements on the material studied.
 

 
Task for the 4th Pair
 
1. Read the text.
2. Highlight the similarities and differences between the gravitational and electrostatic fields.
3. Prepare a presentation for the class.
4. Prepare two false and true statements on the material studied.

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Task for the 5th Pair
 
1. Read the text.
2. Highlight the similarities and differences between the gravitational and electrostatic fields.
3. Prepare a presentation for the class.
4. Prepare two false and true statements on the material studied.
 

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Consider an electric field between two equally but oppositely charged plates a and b whose separation is small. The electric field would be uniform between these plates.

Electric Potential

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

a

b

-

-

-

-

-

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

a

b

-

-

-

-

-

If we release a charge +q from the positive plate b the electric force would accelerate the charge toward the negative plate.

+q

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Work

The electric field will do work to move the charge across the electric field.
W = ΔKE
The charge has high Electrical Potential Energy near b
As the charge move closer to a, the Electrical PE decreases while the KE increases
The size of PE is dependent on the size of the electric field

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Electric Potential – the electric potential per unit charge between the plates
V for voltage (the symbol and unit are the same)
V = PEelectric/q
It is impossible to find the V at any point in an electric field
We can only measure the difference in potential between two points.

Electric Potential

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Vba = Va - Vb
Vba = PEa/q – PEb/q
Vba = ΔPE/q
ΔPE = qVb
ΔU = qV
Where ΔU is the transformation of PE to KE and vice versa.

Electric Potential

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Vba = W/q
where W is the net work to move the charge across the magnetic field.
The unit for voltage is Joules/Coulomb, or simply Volts in honor of Alessandro Volta.

Electric Potential and Work

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

We define the direction of the electric field as originating at areas of high potential (the positive plate in the picture) and ending at areas of low potential (the negative plate)

Electric Potential and Direction

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Often the areas of low potential are assigned a Zero value.
Called ground.

Electric Potential and Direction

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

A positive charge is moved from the positive plate to the negative plate
Does the charge gain potential (+voltage) or lose it (-voltage)
Is the change in the PEelectric positive or negative?
Is the work done by the electric field positive or negative?

Scenario I

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Negative
Negative
Positive - Wnet is positive (force is in the same direction as displacement)

Answer

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

A positive charge is moved from the negative plate to the positive plate.
Does the charge gain potential (+voltage) or lose it (-voltage)
Is the change in the PEelectric positive or negative?
Is the work done by the electric field positive or negative?

Scenario II

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Positive
Positive
Negative(force is in opposite direction of displacement)

Answer

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

A negative charge moves from the negative plate to the positive plate.
Does the charge gain potential (+voltage) or lose it (-voltage)
Is the change in the PEelectric positive or negative?
Is the work done by the electric field positive or negative?

Scenario III

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

Positive
Negative
Positive

Answer

PHY_10_35_V2_P_COMPARISON OF GRAVITATIONAL AND ELECTROSTATIC FIELDS