An engineer in a marine research laboratory is testing a new uniform copper-alloy umbilical cable designed for deep-sea sensors. They set up a test circuit using a safety-regulated 4.5 V4.5\text{ V}4.5 V DC power supply, an ammeter, a voltmeter, and a sample length of the alloy cable.
Explain why a 4.5 V4.5\text{ V}4.5 V power supply does not present an electrical shock hazard to the laboratory engineer.
At a cable sample length of 1.50 m1.50\text{ m}1.50 m, the current flowing through it is 0.75 A0.75\text{ A}0.75 A and the measured potential difference across this section is 3.6 V3.6\text{ V}3.6 V. Calculate the electrical resistance of this 1.50 m1.50\text{ m}1.50 m length of cable.
Assuming the temperature of the alloy cable remains constant, use the direct proportionality between the cable's length and its resistance to predict the resistance of a 4.50 m4.50\text{ m}4.50 m length of the same cable.
39 exam-style questions on AQA GCSE Physics 2.1 Current, potential difference and resistance, covering 2.1.1 Standard circuit diagram symbols, 2.1.2 Electrical charge and current, 2.1.3 Current, resistance and potential difference, and 2.1.4 Resistors. Each one has a worked solution and a mark scheme showing where the marks go.