Class 6 Flashcards
A positive charge will move towards ______ electric potential and a negative charge will move towards _______ electric potential.
Positive = lower Negative = higher
Flow rate of charge, current:
I = ?
Q/t
What are the units of current?
Amp, A = C/s
coulomb per second
Current is defined as the movement of _______ charge.
Positive
What is Ohm’s law?
V = IR
How do you calculate resistance, R?
R = rho L/A
rho = "resistivity" an intrinsic property of the material L = length A = cross sectional area
What is the unit for resistance, R?
Ohm
How do you calculate total resistance for resistors in series?
Req = R1 + R2 + R3
Resistors in series have the same ______ across/through each.
Current
Resistors in paralle have the same _______ across/through each.
Voltage
How do you calculate total resistance for resistors in parallel?
1/Req = 1/R1 + 1/R2 + 1/R3
Current into and out of any point in a circuit must equal what?
Zero
The sum of voltages around any closed loop in a circuit must equal what?
Zero
When traveling around a circuit, what end of the battery does current start?
Positive
P = ? = ? = ?
How do you know which to use?
P = IV = I^2R = V^2/R
Use whichever is convenient, keeping in mind the situation and Kirchoff’s rules
Describe a voltmeter
Measures
voltage
Connects in parallel to circuit segment of interest
High internal resistance
Describe an ammeter
Measures current
Connects in series to circuit segment of interest
Low internal resistance
Real batteries have internal resistance. How is that quantified?
V = epsilon - Ir
episoln = emf, "ideal voltage" r = internal resistance
Magnetic field exert forces on moving charges:
Fb = ?
Fb = |q|vB sin(theta)
B = magnetic field theta = angle between v and B
Does a charge exert an electric force regardless of whether or not it is moving?
Yes
Does a charge exert a magnetic force regardless of
whether or not it is moving?
No! A charge will not exert a magnetic force unless it is in motion
What is the unit of magnetic field strength?
Tesla
What is the Right Hand Rule for determining direction of magnetic force?
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
Is there any magnetic force if v and B are parallel?
No
