14 7 A student connected the output from a source of alternating potential difference (p.d.) to a series resistor combination. She connected an oscilloscope across the 150 Ω resistor as shown. V 120 Ω 150 Ω oscilloscope (a) The trace obtained on the oscilloscope is shown below. (i) Determine the peak p.d. across the 150 Ω resistor. y-sensitivity of oscilloscope = 2.0 V per division (2) ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... Peak p.d. across 150 Ω resistor = ....................................................... Turn over 15 (ii) Calculate the root mean square (r.m.s.) value of the current in the circuit. (3) ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... r.m.s. value of current = ....................................................... (iii) Calculate the power dissipated in the circuit. (3) ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... Power dissipated in circuit = ....................................................... (b) Another student suggested that a voltmeter would be more accurate than using an oscilloscope to determine the magnitude of the p.d. Comment on this suggestion. (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (Total for Question 7 = 11 marks)