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(R, +R,) I)
1(1) = 10 exp( L
(c) Using your results from (b), find the value of the total emf around the circuit (which
from Faraday's law is -Ldl / dl) just after the switch is opened. Is your assumption in (b)
that Go could be ignored for times just after the switch is opened OK?
dIU)1
G=-L--
dt ,.0
=Io(R, +R,)
S· mce 10 =­
Go
,
R '
Go (R, )
G= - (R, +R, )= 1+- Go »Go
R, R,
(": R, »R,)
Thus, the assumption that Go could be ignored for times just after the switch is open is
OK.
(d) What is the magnitude of the potential drop across the resistor R, at times t > 0, just
after the switch is opened? Express your answers in terms of Go , R" and R, . How does
the potential drop across R, just after t = 0 compare to the battery emf Go, if
R, =100R,?
The potential drop across R2 is given by
If R, = 1 OOR"
R, (R, )( R, ) R,
L'>.V, = G= 1 +- Go =-Go
R, + R, R, + R, R, R,
i1V 2 = 100 Eo
This is why you have to open a switch in a circuit with a lot of energy
stored ill the magnetic field very carefully, or you end lip very dead!!