In the circuit from the preceding question, what is the equivalent resistance be

Question

In the circuit from the preceding question, what is the equivalent resistance between points a and c? (Please read the question carefully: this is not a repeat of the previous question.) Select one: A solenoid of length 15 cm consists of a wire wrapped tightly around a wooden core. The magnetic field strength is 1.0 T inside the solenoid. If the solenoid is stretched to 27 cm by applying a force to it, what does the magnetic field become? Select one: The resistivity of gold is 2.44 x 10^-8 ohm.m at room temperature. A gold wire that is 1.4 mm in diameter and 16 cm long carries a current of 250 mA. What is the electric field in the wire? Select one: A. 0.0051 V/m B. 0.0040 V/m C. 0.0031 V/m D. 0.00099 V/m E. 0.0099 V/m

Explanation / Answer

Q15.
between a and c:

the 10 ohm ressitance wont come into picture

so 30 ohms and 60 ohms are in series==> net ressitance=90 ohms
it is in parallel with 10 ohms

then net resistance=90*10/100=9 ohms

so option B is correct.

Q23.as we know magnetic field inside solenoid is given by

B=mu*N*I/L
where mu=4*pi*10^(-7)

N=number of turns

I=current

L=length

with everything else constant, magnetic field will vary inversely with length.

then B*L=constant

hence 1*0.15=B*0.27

B=0.15/0.27=0.5556

or equivalent to 0.6 T

hence option E is correct.

Q26.

as we know

current density per cross sectional area=conductivty*electric field

and conductivity=1/resistivity

hence current/(pi*radius^2)=(1/resistivity)*electric field

putting the values

we get electric field=0.004 V/m

hence option B is correct.

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