Yr 12 2.7 Int Nature Ans 03

New Zealand Institute of Physics

ASSESSMENT SCHEDULE

Achievement Standard 2.7

“Calling CQ”

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.

Question ONE

Evidence

Achievement

T = 1 / f = 1.4 x 10-7 s

2

Correct answer

Wavelength = v / f = 42 m

2

Correct answer

Any two of: microwaves, infrared, visible light (light ok), ultraviolet, x-ray and gamma ray.

1

Both correct

Merit

(a) (b) (c)

(d)

Used d=vt but did not allow for return journey

d = v t where t = 2.56 s / 2 to account for round trip time. d = 3.8 x 108 m. Two (a) (b)

Bending of a wave as it moves from one medium to another.

n1 v 2 λ 2 = = n2 v 1 λ 1

1

Correct definition

2

Correct answer

wavelength ionised = wavelength lower x

1 .0 = 22 m 0 .9

Physics 2.3 Assessment Schedule

2

Correct answer

Excellence

Unchanged

1

Correct answer

(d)

Waves refract away from the normal when passing from a medium with a larger refractive index into a medium with a lower refractive index.

1

Correct answer = away

Question

Evidence

(c)

(e)

(f)

Three (a)

n ionised sin ( θ ionised ) = n lower sin (θ θ lower = Sin-1 (n ionised / n lower ) = 64°

lower

If the angle of incidence of the transmitted radio waves exceeds the critical angle, the waves undergo total internal reflection and are thereby directed back towards the Earth. This will result in the radio signals being received beyond the horizon of the transmitter at a distance dependent on the height of the ionised layer, the ratio of the refractive indices and the angle of incidence. T = 24 hr x 60 min x 60 s = 86,400 = 8.6 x 104 s

(b)

v = d t = 2π R / T = 3.0 x 103 ms-1

(c)

a = v2 / R = 0.22 m s -2 F = m a = 9.1 N

(d)

(e)

):

Correct explanation for bending away

Achievement

Merit

Idea that refracted angle must be 90 degrees

Achieved + incorrect use of Snell’s law

2

Correct answer

Knowledge of TIR and link to increased distance.

1

Clear understanding of TIR and link to increased distance.

2

Correct answer

1

One clear explanation given.

Some indication of TIR

2

1

1

Correct answer Incorrect answer used height not radius

2

Correct answer

Incorrect answer used height not radius

Velocity vector tangent to the circle. Acceleration and Force vectors directed towards the centre of the circle The satellite remains in a fixed position above the rotating Earth. An antenna pointed at a satellite will remain so, and requires no tracking mechanism.

Excellence

Two of three vectors correct

1

All correct

1

General understanding of reason given.

A geostationary satellite at a high altitude will have a greater line-of-sight to places distant from the point of transmission. This will allow for much longer transmission paths than a low orbiting satellite. A low orbiting satellite with a period of less than 24 hours will only be in view of a particular location on Earth for part of the time. A geostationary satellite will always be accessible to a given location on Earth, and thus can provide uninterrupted communications.

Total Opportunities:

Criterion 1: 4

Criterion 1: 4

Criterion 1: 2

Criterion 2: 4

Criterion 2: 2

Criterion 2: 2

Physics 2.3 Assessment Schedule

Sufficiency Statement The grade awarded is the highest one that has been demonstrated in all achievement criteria up to and including that grade. The following is a guide to the standard required for each grade in the two criteria. Criterion 1: • Achievement is demonstrated if 2 or more aspects of phenomena, concepts or principles are identified or described. • Achievement with merit is demonstrated if descriptions or explanations show understanding of 2 different phenomena, concepts or principles. •

Achievement with excellence is demonstrated if explanations show clear understanding of 1 different phenomena, concepts, principles or relationships.

Criterion 2: • Achievement is demonstrated if 2 different relationships, concepts or principles are used to solve problems. •

Achievement with merit is demonstrated if 1 different relationships, concepts or principles are used to solve problems in situations that are not straightforward.

•

Achievement with excellence is demonstrated if 1 integrations of relationships, concepts or principles lead to the solution of problems.

Physics 2.3 Assessment Schedule