NCEA Level 1 Physics (90185) 2010 — page 1 of 3
Assessment Schedule – 2010 Version dated: 3011
Physics: Demonstrate understanding of electricity and magnetism (90185)
Note: Minor computational errors will not be penalised. A wrong answer will be accepted as correct provided there is sufficient evidence that the mistake is not due to a lack of understanding. Such evidence includes:
• the last written step before the answer is given has no unexpanded brackets or terms and does not require rearranging.
• the power of any number that is multiplied by a power of 10 is correct.
Correct units and significant figures are required only in the questions that specifically ask for them.
Italics indicate replacement evidence.
Evidence Statement
Q Evidence Achievement Achievement with
Merit Achievement with Excellence ONE
(a)
1 Correct charge distribution.
NB: any mingling of – with + in “N”
(b) Like charges repel.
The negative charges in the cloud repel the negative charges on the surface of the ground, leaving the surface positively charged.
1 Mentions electron repelling each other to leave ground positive.
Any mention or
implication that protons move is “N”, this includes that opposites attract
1 Achievement plus correct explanation that it is due to like charges repelling.
(c) From the cloud to the ground (downwards).
Because the electrons or negative charges are free to move in atoms (the positive charges are bound to the nucleus).
OR
Positive ions in air move upward.
1 Correct direction or explanation.
1 Correct direction and explanation.
NB focus on the reason why the electrons can move and the protons can’t
(d)
R=V
I = 30 000 000
120 000 =250 Ω Resistance per km =250
6.1 =40.98
=41 Ω km−1
2 Correct working and answer for 250 Ω. Take care of powers of ten.
0.25 Ω is OK for “A”
but no further OR
Correct method for the second step.
2 Correct working and answer for
41 Ω km–1.
(e)
P= E
t = 9.5×106
2.0×10−4 =4.75×1010 W V = P
I =4.75×1010
8 000 =5 937 500 V
=5 937.5 kV
=5 938 kV
2 Correct working and answer for power.
OR
ONE correct calculation eg conversion to kV done correctly even if value is incorrect due to previous incorrect calculations.
2 Correct working answer for voltage in volts.
2 Correct working and answer for voltage in kilovolts.
NCEA Level 1 Physics (90185) 2010 — page 2 of 3 (f)
2 Rearranged the formula correctly and shows correct substitution.
2 Correct working and answer for d.
(g) 1. A lightning conductor is a metal rod attached to the highest point on a building and is connected to the ground by a thick metal strip.
2. Lightning usually follows the shortest and easiest path – the lightning rod provides this path.
3. When the lightning strikes, the current flows through the metal to the ground rather than through the building, thereby protecting the building.
1 Mentions one key idea. 1 Achievement plus gives a general reasoning as in 2.
1 Achievement plus gives a scientific reasoning as in 3.
TWO
(a)
2 Correct formula and working only.
(b)
Voltage across the heater B is
= 8.0 V
Current through heater B
= 3.5 – 2.0 = 1.5 A
2 Correct answer for voltage or current.
2 Correct working and answer for voltage and current.
2 Correct working and answer.
(c) Ohm’s law states the ratio of V/I is the resistance.
1. Between 0 and 10 V, the graph is a straight line, so the resistance remains constant.
( ).
2. Between 10 V and 17 V the
resistance decreases, because the V/I ratio is the resistance and it decreases OR uses the approximate calculations to find the resistance of graph segments, eg
R(10−15 V)=V I = 4
0.20=20 Ω R(15−18 V)=V
I = 4
0.40=10 Ω OR any other correct calculations shown.
1 Either states resistance is constant between 0- 10 V range
OR
States resistance decreases between 10 – 18 V range.
1 States resistance is constant over the range 0 to 10V.
AND
States resistance decreases over the range 10 to 18 V.
1 Explains both sections of the graph correctly with correct calculations.
(d) When the voltage is 10 V, current = 0.20 A.
P = VI = 10 × 0.20 = 2.0 W
2 Correct answer for the
current.
2 Correct working and
answer.
NCEA Level 1 Physics (90185) 2010 — page 3 of 3
(e) RT = R1 + R2 + R3
= 365 + 25 + 280 = 670 Ω
Voltage across the thermistor V = IR = 0.0179 × 280 = 5.0 V
2 Correct working and answer for total resistance.
Beware of rounding to give different final values
2 Correct working and answer for total current.
2 Correct working and answer for
thermistor voltage.
THREE
(a) Since the like poles are nearer to one another the repulsive forces are stronger than the attractive ones. (Hence the resultant force is repulsive.)
1 Mentions the repulsive force is stronger. (Do not accept the answer
‘there is a repulsive force’).
1 Correct explanation.
(b)
1 Shows the correct polarity or correct
shape.
1 Both shape and
direction are correct.
3(c) 1. The rods move away from each other.
2. Both rods will be magnetised when the current flows through the coil.
3. The adjacent ends of the rods will have the same polarity. Since like poles repel, the rods will move away from each other.
1 The rods move away from each other OR
Recognise that the rods have become
magnetised.
NB: Talk of charging
“N”
1 Need both
achievement points.
1 Correct explanation in terms of same polarity.
Judgement Statement
Achievement Achievement with Merit Achievement with Excellence
A minimum of 8 A or higher, which must include a minimum of 3 from each criterion
A minimum of 10 correct including 6 M or higher, which must include a minimum of 3 from each criterion
A minimum of 12 correct including at least 3 M or higher from each
criterion, and 3 E, with at least 1 from each criterion
