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EMF
7.12
A steady electric current I flows around a circuit containing
a battery of voltage V and a resistor
r rR. Which of the
following statements about E ⋅ dl is true?
∫
A. It is zero around the circuit because it’s an electrostatic field
B. It is non-zero around the circuit because it’s not an
electrostatic field
C. It is zero around the circuit because there is no electric field
in the battery, only in the rest of the circuit
D. It is non-zero around the circuit because there is no electric
field in the battery, only in the rest of the circuit!
E. None of the above
7.13
EMF = ∫
r r
f ⋅ dl
EMF is the line integral of the total force
per unit charge around a closed loop.
The units of EMF are:
A)
B)
C)
D)
E)
Farads
Joules.
Amps, (that’s why current flows.)
Newtons, (that’s why it’s called emf)
Volts
7.14
Imagine a charge q able to move around a tube which
makes a closed loop. If we want to drive the charge around
the loop, we cannot do this with E-field from a single
stationary charge.
+ q
Can we drive the charge
around the loop with
some combination of
stationary + and –
charges?
A) Yes
B) No
+
7.16
EMF = ∫
r r
f ⋅ dl
Is there a nonzero EMF around the (dashed) closed loop,
which is partway inserted between two charged isolated
capacitor plates?
++++++++++++++++
---------------A) EMF=0 here
B) EMF≠0 here
C) ? I would need to do a nontrivial calculation to decide
7.15
A circuit with an ideal battery (no resistance) with voltage
difference ∆V is attached to a resistor. The force per charge
due to the charges is E. The force per charge inside the
battery is f = fbat + E
How many of the following statements are true?
v v
emf = ∫ f ⋅ d l
B
emf =
∫
A(insi de bat )
B
A
v
v
emf = ∫ f bat ⋅ d l
v
v
f bat ⋅ d l
v v
emf = ∫ E ⋅ d l
A
B
A)
B)
C)
D)
E)
0
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2
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