Thermistor Circuit (1)

Electricity and Magnetism Level 3

In the circuit above, if both switch $S_1$ and switch $S_2$ are open, calculate the voltage difference in volts between node $A$ and node $B$ at $25^\circ C$ ( $V_A-V_B$ ). (The resistance of the thermistor $R_T$ is $1875\ \Omega$ at $25^\circ C$ ).

Try also part 2 and part 3 .

The answer is -7.

2 solutions

Charley Shi
Nov 12, 2020

Current can only flow through resistors $R_1$ through $R_4$ since both switches are open. These resistors are in series so current through all of these resistors is $I_s = 2\textrm{mA}$ .

The voltage at node A in terms of the voltage at node B: $V_A = V_B - I_s(R_2+R_4)$ $V_A - V_B = - I_s(R_2+R_4) = -2(1.5 + 2)$ $= \boxed{-7\textrm{V}}$

In part 2, did you purposely omit the value of $R_S$ ?

Steven Chase - 7 months ago

There's no $R_s$ ?

Charley Shi - 7 months ago

Ah, so it is $R_5$ . Thanks

Steven Chase - 7 months ago

@Charley Feng , I got non-integer answer for part 2. Can you check?

Chew-Seong Cheong - 7 months ago

My answer is correct.

Charley Shi - 7 months ago

Chew-Seong Cheong
Nov 13, 2020

The voltage difference $V_{AB} = (1.5+2)(-2) = \boxed{-7} \ \rm V$ .

Thermistor Circuit (1)

The answer is -7.

2 solutions

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