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NCEA Level 2 Physics (90257) 2011 — page 1 of 4 Assessment Schedule – 2011 Physics: Demonstrate understanding of electricity and magnetism (90257) Evidence Statement Q Evidence Achievement The left hand plate, A. Field lines go from positive to negative. OR Field lines show the direction a positive test charge would move. 1 ONE part correct. (b) The field lines are equally spaced. 1 Correct answer. (c) V d V = Ed 2 2 ONE (a) E= Merit 1 BOTH parts correct. Correct working except for ONE error. 2 Correct answer. Correct calculation of energy change. 2 Correct working with ONE error. Excellence V = 3.33 ´ 106 ´ 0.12 V = 399 600 = 4.0 ´ 105 V = 400 kV (d) V= DE q DE = Vq DE = 4 ´ 10 ´ 1.5 ´ 10 5 -10 DE = 6 ´ 10-5 J EK = v= 1 2 mv 2 = 6 ´ 10-5 J 2 ´ 6 ´ 10 -5 2.5 ´ 10-2 = 4.8 ´ 10 -3 = 0.069 m s -1 OR F = 4.995 10–4 a = 0.01998 2 Correct working and answer. NCEA Level 2 Physics (90257) 2011 — page 2 of 4 (e) TWO (a) (b) When the ball touches the negative plate, it will gain electrons until it has an overall negative charge. It then experiences a force in the opposite direction to the field (OR is attracted to the positive plate OR is repelled from the negative plate). When the ball touches the positive plate, it loses electrons until it has an overall positive charge. It then experiences a force in the same direction as the field (OR is attracted to the negative plate OR is repelled from the positive plate). 1 Electrons flow from the negative terminal in the direction X→Y These electrons are cutting across a magnetic field that is towards the bottom of the page. Each electron experiences a force in the direction “A” This causes the wire to experience a force and to swing in direction “A” OR can explain in terms of conventional current. 1 V = IR 1 ONE correct idea. Eg moves towards positive plate The loop swings in direction “A”. 1 Moves towards + and attraction/force/repulsion 1 Direction of charge flow and loop movement correct. 1 Full explanation linking the charging process and the force due to the field. ONE correct calculation. 2 All correct except for ONE error. Full explanation. Loop movement + Current flow + perpendicular / cutting / across (not in). OR Current direction and wire perpendicular/crossing/cutting (not in) field. V R 6.0 I= = 3.33 A 1.8 F = BIl 2 Correct answer. Must have = 3.8 cm. Stops at 0.038 m. F 0.25 = BI 2.0 ´ 3.33 l = 0.038 m l= Electron – direction “C” (or left). TWO correct ideas. M+ Electron movement and repetition I= (c) 1 1 Correct answer. NCEA Level 2 Physics (90257) 2011 — page 3 of 4 (d) V = Bvl 1 Correct except for one error. 1 Correct answer. (Must link power of 5W to 12V) 2 Correct answer. 1 Correct LED current AND ONE reason. V = 12 - 3.40 = 8.6 V 2 Correct answer. Must state 2 Sig Fig. 1 Correct answer. 2 Correct answer. 1 Correct LED current AND BOTH reasons. V Bl 11´ 10-3 v= 2 ´ 0.0375 v= v = 0.1467 = 0.15 m s-1 THREE (a) (b) When the bulb has 12 V across it, the power output is 5 W. P = VI P V 5 I= = 0.42 A 12 I= (c) LED “B” is forward biased, so that the resistance is small (as long as the voltage is greater than the knee voltage) so current will flow through it. LED “A” is reverse biased so that the resistance is infinite (very large) (as long as the voltage is less than the break down voltage), so no current will flow through it. OR LED “B” has low resistance, so the current through it is large. LED “A” has infinite/large resistance, so the current through it is zero. (d) NCEA Level 2 Physics (90257) 2011 — page 4 of 4 (e) If a third LED is added in parallel, this will decrease the total resistance (of the circuit). The supply voltage doesn’t change, so the total current (and therefore the resistor current) increases. V = IR, so the voltage across the resistor will increase. 1 ONE correct idea. Voltage increases. Voltage +1 idea (f) V 3.5 5.0 (Must be 5 – no other option). I 0.7 OR if tangent drawn then R=0.6 2 Correct answer. (g) As the current increases, resistance decreases. 1 Correct answer. R 1 TWO correct ideas. 1 Full explanation including all THREE ideas linked. Judgement Statement Achievement Achievement with Merit Achievement with Excellence 2 A1 + 2 A2+ 4 A 1 M1 + 1 M2 + 11 A 1 E1 + 1 E2 + 1 E + 10 A OR 4E+8A Note: where the criterion is not specified, the required grade(s) can be from either.