Class 6

Question 1

A positive charge will move towards ______ electric potential and a negative charge will move towards _______ electric potential.

Answer 1

Positive = lower
Negative = higher

Question 2

Flow rate of charge, current:

I = ?

Answer 2

Q/t

Question 3

What are the units of current?

Answer 3

Amp, A = C/s

coulomb per second

Question 4

Current is defined as the movement of _______ charge.

Answer 4

Positive

Question 5

What is Ohm’s law?

Answer 5

V = IR

Question 6

How do you calculate resistance, R?

Answer 6

R = rho L/A

rho = "resistivity" an intrinsic property of the material
L = length
A = cross sectional area

Question 7

What is the unit for resistance, R?

Answer 7

Ohm

Question 8

How do you calculate total resistance for resistors in series?

Answer 8

Req = R1 + R2 + R3

Question 9

Resistors in series have the same ______ across/through each.

Answer 9

Current

Question 10

Resistors in paralle have the same _______ across/through each.

Answer 10

Voltage

Question 11

How do you calculate total resistance for resistors in parallel?

Answer 11

1/Req = 1/R1 + 1/R2 + 1/R3

Question 12

Current into and out of any point in a circuit must equal what?

Answer 12

Zero

Question 13

The sum of voltages around any closed loop in a circuit must equal what?

Answer 13

Zero

Question 14

When traveling around a circuit, what end of the battery does current start?

Answer 14

Positive

Question 15

P = ? = ? = ?

How do you know which to use?

Answer 15

P = IV = I^2R = V^2/R

Use whichever is convenient, keeping in mind the situation and Kirchoff’s rules

Question 16

Describe a voltmeter

Answer 16

Measures
voltage
Connects in parallel to circuit segment of interest
High internal resistance

Question 17

Describe an ammeter

Answer 17

Measures current
Connects in series to circuit segment of interest
Low internal resistance

Question 18

Real batteries have internal resistance. How is that quantified?

Answer 18

V = epsilon - Ir

episoln = emf, "ideal voltage"
r = internal resistance

Question 19

Magnetic field exert forces on moving charges:

Fb = ?

Answer 19

Fb = |q|vB sin(theta)

B = magnetic field
theta = angle between v and B

Question 20

Does a charge exert an electric force regardless of whether or not it is moving?

Answer 20

Yes

Question 21

Does a charge exert a magnetic force regardless of

whether or not it is moving?

Answer 21

No! A charge will not exert a magnetic force unless it is in motion

Question 22

What is the unit of magnetic field strength?

Answer 22

Tesla

Question 23

What is the Right Hand Rule for determining direction of magnetic force?

Answer 23

With right hand:

Thumb in direction of v
Fingers (not bent) in direction of B
Palm will give you the direction of Fb for a POSITIVE charge

Back of hand will give you direction of Fb for a NEGATIVE charge

Question 24

Is there any magnetic force if v and B are parallel?

Answer 24

No

Question 25

Can magnetic forces do work?

Answer 25

No NO NO, NEVER!

Question 26

What creates magnetic fields?

Answer 26

Moving charges

Question 27

How do you use the Right Hand Rule for determining the direction of the magnetic field?

Answer 27

1. Point thumb in the direction of the current

2. Curl fingers around; direction of fingers = direction of the field