1. Electric Forces
Physics A
Static #3

2. Learning Targets
I can attribute the change in the electric force between charged objects with the changes in the distance between them and/or the magnitude of the charges.
I can calculate the electric force between two charged objects when given the charges of the objects and the distance between them.
I can explain why acquiring a large excess static charge affects your hair.

3. Force as a Vector Quantity
The electrical force is expressed using the unit Newton.
Being a force, the strength of the electrical interaction is a vector quantity that has both magnitude and direction.
The direction of the electrical force is dependent upon whether the charged objects are charged with like charge or opposite charge.

4. Force as a Vector Quantity
Electrical force has a magnitude or strength.
Electric force can be altered by changing three variables.
First, the quantity of charge on one of the objects will affect the strength of the repulsive force.
The more charged a balloon is, the greater the repulsive force.

5. Force as a Vector Quantity
Second, the quantity of charge on the second object will affect the strength of the force.
Finally, the distance between the two objects will have a significant and noticeable effect upon the repulsive force.
The electrical force is strongest when the objects are closest together.
The magnitude of the force and the distance between the two objects is said to be inversely related.

6. Coulomb’s Law Equation
Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects.
The symbol k is a proportionality constant known as the Coulomb's law constant.
The value is approximately 9.0 x 109 N • m2 / C2.

7. Coulomb’s Law Equation
The Coulomb's law equation provides an accurate description of the force between two point charges.
The symbols q1 and q2 represent the quantities of charge on the two interacting objects.
Since an object can be charged positively or negatively, these quantities are often expressed as "+" or "-" values.
DO NOT USE THE “+” OR “-” VALUES IN THE EQUATION!

8. Suppose that two point charges, each with a charge of +1
Suppose that two point charges, each with a charge of Coulomb are separated by a distance of 1.00 meter. Determine the magnitude of the electrical force of repulsion between them.

9. Two balloons are charged with an identical quantity and type of charge: nC. They are held apart at a separation distance of 61.7 cm. Determine the magnitude of the electrical force of repulsion between them.

10. Two balloons with charges of +3. 37 µC and -8
Two balloons with charges of µC and µC attract each other with a force of Newton. Determine the separation distance between the two balloons.

11. Comparing Electrical and Gravitational Forces
Electrical force and gravitational force are the two non-contact forces.
How are they similar?

12. The Q in Coulomb's law equation stands for the _____.
a. mass of a charged object
b. # of excess electrons on the object
c. the current of a charged object
d. the distance between charged objects
e. charge of a charged object

13. The symbol d in Coulomb's law equation represents the distance from ___. a. A to B b. A to D c. B to C d. B to D e. C to D f. A to G g. B to F h. C to E

14. Determine the electrical force of attraction between two balloons that are charged with the opposite type of charge but the same quantity of charge. The charge on the balloons is 6.0 x 10-7 C and they are separated by a distance of 0.50 m.

15. Joann has rubbed a balloon with wool to give it a charge of -1
Joann has rubbed a balloon with wool to give it a charge of -1.0 x 10-6 C. She then acquires a plastic golf tube with a charge of +4.0 x 10-6 C localized at a given position. She holds the location of charge on the plastic golf tube a distance of 50.0 cm above the balloon. Determine the electrical force of attraction between the golf tube and the balloon.

16. A balloon with a charge of 4. 0 µC is held a distance of 0
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.

17. At what distance of separation must two 1
At what distance of separation must two 1.00-microCoulomb 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?

18. Cause & Effect Relationships
Careful observation and measurement might indicate that a pattern exists in which an increase in one variable always causes another measurable quantity to increase.
This type of cause-effect relationship is described as being a direct relationship.
In electrostatics, the electrical force between two charged objects is directly related to the magnitude of charge of the two objects.
Increasing the charge of the objects increases the force of attraction or repulsion between the objects.

19. Cause & Effect Relationships
Observation might also indicate that an increase in one variable always causes another measurable quantity to decrease.
This type of cause-effect relationship is described as being an inverse relationship.
In electrostatics, the electrical force between two charged objects is inversely related to the distance of separation between the two objects.
Increasing the separation distance between objects decreases the force of attraction or repulsion between the objects.

20. Cause & Effect Relationships
Electric force is very sensitive to distance.
The pattern between electrostatic force and distance can be further characterized as an inverse square relationship.
The factor by which the electrostatic force is changed is the inverse of the square of the factor by which the separation distance is changed.
If the separation distance is doubled, then the electrostatic force is decreased by a factor of four (22).
If the separation distance is tripled, then the electrostatic force is decreased by a factor of nine.

21. Two charged objects have a repulsive force of 0. 10 N
Two charged objects have a repulsive force of 0.10 N. If the charge of one of the objects is doubled, then what is the new force?

22. Two charged objects have a repulsive force of 0. 10 N
Two charged objects have a repulsive force of 0.10 N. If the charge of both of the objects is doubled, then what is the new force?

23. Two charged objects have a repulsive force of 0. 10 N
Two charged objects have a repulsive force of 0.10 N. If the distance separating the objects is doubled, then what is the new force?

24. Two charged objects have a repulsive force of 0. 10 N
Two charged objects have a repulsive force of 0.10 N. If the distance separating the objects is tripled, then what is the new force?

25. Two charged objects have an attractive force of 0. 10 N
Two charged objects have an attractive force of 0.10 N. If the distance separating the objects is quadrupled, then what is the new force?

26. Two charged objects have a repulsive force of 0. 10 N
Two charged objects have a repulsive force of 0.10 N. If the distance separating the objects is halved, then what is the new force?

27. Two charged objects have a repulsive force of 0. 10 N
Two charged objects have a repulsive force of 0.10 N. If the charge of one of the objects is doubled, and the distance separating the objects is doubled, then what is the new force?

28. Two charged objects have a repulsive force of 0. 10 N
Two charged objects have a repulsive force of 0.10 N. If the charge of both of the objects is doubled and the distance separating the objects is doubled, then what is the new force?

29. Two charged objects have an attractive force of 0. 10 N
Two charged objects have an attractive force of 0.10 N. If the charge of one of the objects is tripled and the distance separating the objects is tripled, then what is the new force?