Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
19 Omission Where a candidate response is incomplete, marks should be awarded for relevant points that are included. Example/comment Questions requiring candidates to give an explanation. Marking scheme indicates four points are required each worth ½ mark. Candidates response includes up to three correct points. Candidates could achieve ½, 1, 1½. Marking symbol Inverted V where information is omitted Question: Use the kinetic model to explain what happens to the pressure of the trapped air as its volume decreases. Assume its temperature remains constant. Marking scheme gives four ½ marks; More frequent collisions ½ with the wall ½ greater force ½ greater pressure ½ Response: “More frequent collisions with the walls cause a greater pressure.” Award 1½/2 more frequent collisions with the walls cause a greater pressure. ^ Inverted V Where information is omitted. Credit should be given where the omitted information can be readily inferred from the response. Question: Calculate the current in a 20 Ω resistor when voltage of 5 V is supplied. Response: “I = 5/20 = 0.4” In this case the candidate has used the correct formula but has omitted to write down the formula. Award ½ mark for the formula, ½ mark for correct substitution into implied formula. I = 5/20 = 0.4 Tick beside substitution Straight line through final answer Example/comment Question: Candidate is asked to find number of lines per metre on the grating. Marking schedule allows three marks. First fringe 37° Central fringe nλ = d sin θ (1/2) 1 x 633 x 10 − 11 = d sin 37 (1/2) for λ, (1/2) for n d = 1.05 x 10 − 6 (1/2) lines/m = 1.05 x 10 5 (1) Response: 633x 10 −9 = d sin 37 ^ This gets (11/2) marks ½ for implied formula ½ for correct n ½ for λ Candidates must answer the question posed correctly before the marks can be awarded for an explanation. A correct explanation or justification without the correct answer or no answer is awarded 0 marks, if the question states candidates must justify their answer. Example/comment Question: Candidate is asked to explain what happens to the reading on a voltmeter connected across battery with internal resistance when a second resistor is added in parallel. Response: Increase (1/2) Resistance in circuit less (1/2) Current increases (1/2) Lost volts increases (1/2) Award (2) marks Response: Resistance in circuit less Current increases Lost volts increases Award (0) marks Inverted V Where information is omitted