Self Test on Tutorial 5 A lamp has a p.d. of 12 V across it.  Calculate how much electrical energy is transferred when:  A charge of 400 C passes through it; A current of 2.5 A passes through it for 30 s                                             A 230 V electric heater takes a current of 2.0 A.  Calculate the heat produced if it is switched on for 5.0 minutes.                                                                   Calculate the p.d. across a wire if the energy transferred is: 600 J when a charge of 50 C passes through it; 450 J when there is a steady current of 0.5 A flowing for 20 s.             A 230 V kettle transfers 6.9 × 105 Joules of energy in 5.0 minutes.  What is the current in the kettle?                                                                                                    What is the p.d. across a wire of resistance 8.0 W when there is a current of 1.5 A flowing through it? What is the resistance of a wire if a potential difference. of 6.0 V drives a current of 0.25 A through it?     A p.d. of 3.0 V is applied across a wire of resistance 15 W.  What is the current in the wire?                                                                                                    The resistivity of copper is 1.7 × 10-8 Wm.  Calculate the resistance of 50 m of copper cable with a cross-sectional area of 2.5 × 10-6 m. What is the voltage drop across this cable if it carries a current of 13amps?                                                                                                              The resistivity of nichrome is 1.1 × 10-6 Wm.  Calculate the lengths of 0.4 mm diameter nichrome wire needed to make coils of resistance: 2.0 W; 5.0 W