Chapter 1.4, Problem 75ES

According to Ohm’s law, when a voltage of $V$ volts is applied across a resistor with a resistance of $R$ ohms, a current of $I=V/R$ amperes flows through the resistor.

(a) How much current flows if a voltage of $3.0$ volts is applied across a resistance of $7.5$ ohms?

(b) If the resistance varies by $\pm 0.1$ ohm, and the voltage remains constant at $3.0$ volts, what is the resulting range of values for the current?

(c) If temperature variation cause the resistance to vary $\pm \delta$ from its value of $7.5$ ohms, and the voltage remains constant at $3.0$ volts, what is the resulting range of values for the current?

(d) If the current is not allowed to vary by more than $\in =\pm 0.001$ ampere at a voltage of $3.0$ volts, what variation of $\pm \delta$ from the value of $7.5$ ohms is allowable?

(e) Certain alloys become superconductors as their temperature approaches absolute zero $\left(-273°\text{C}\right),$ meaning that their resistance approaches zero. If the voltage remains constant, what happens to the current in a superconductor as $R\to 0^{+}$ ?