QUESTION 1



Grade 12 PHYSICAL SCIENCES - CONTROL TEST

Time: 90 minutes Marks: 90

Answer all questions on the paper provided.

Write on both sides of the paper.

Non-programmable calculators may be used.

Refer to the data sheet where necessary.

Attach your question paper to the back of your script.

QUESTION 1

Various possible answers are provided for each question. Write the letter only of the correct answer next to the corresponding number.

1.1 The formula of the organic product formed when methanol reacts with ethanoic acid is:

A C2H4O2

B C3H5O2

C C3H6O2

D C4H8O2 (2)

1.2 The fermentation of sugar solutions using enzymes in yeast can be represented as follows:

|C6H12O6 (aq) |+ |Enzymes |( |CO2 (g) |+ |X |

The product X can be used as a fuel and is a/an …

A Alkane.

B Alcohol.

C Ester.

D Carboxylic acid. (2)

1.3 The pitch of a blaring hooter on a fast-moving minibus taxi travelling at a constant velocity of x m.s–1 changes as it passes an observer. If the frequency of the sound on the minibus taxi is y, and the speed of sound in air is z m.s–1, the frequency the observer hears as the taxi travels towards him is …

A [pic]

B [pic]

C [pic]

D [pic] (2)

1.4 A glass prism disperses white light into a ROYGBIV spectrum because of differences in the speed of light of different frequencies in glass. Which one of the following combinations best describes the dispersion of violet light?

| |Speed in glass |Wavelength |Angle of deviation |

|A |Least |Shortest |Smallest |

|B |Most |Longest |Smallest |

|C |Least |Shortest |Largest |

|D |Most |Longest |Largest |

(2)

1.5 As waves in a ripple tank pass through two narrow openings alongside each other, a distinctive pattern is formed. The phenomena represented by this pattern are …

A interference and diffraction.

B refraction and interference.

C refraction and reflection.

D refraction and dispersion. (2)

1.6 Three resistors of 3 Ω each are connected as shown in the following diagram.

[pic]

What is the effective resistance between points P and R?

A 1 Ω

B 2 Ω

C 3 Ω

D 9 Ω (2)

1.7 You push the south pole of a bar magnet into end X of a long solenoid. The ammeter that is connected to the solenoid shows a deflection to the left.

[pic]

Which additional movement of the bar magnet will produce the same deflection on the ammeter?

A pushing the north pole of the magnet into end X of the solenoid

B pulling the north pole of the magnet out of end X of the solenoid

C pulling the south pole of the magnet out of end Y of the solenoid

D pushing the south pole of the magnet into end X of the solenoid (2)

[14]

QUESTION 2

Complete the following statements by filling in the missing word or phrase.

2.1 A certain concentrated acid is added to sugar and a black porous mass of carbon is formed. The acid is _______________. (1)

2.2 Given a list of methane, ethane, propane and butane, the alkane with the lowest boiling point is ___________. (1)

2.3 People are talking on one side of a doorway. When the sound waves reach the doorway they spread out. This phenomenon is known as ____________. (1)

2.4 Narrowing the width of a slit through which light passes ______________ the amount of diffraction. (1)

2.5 A conductor for which the current in it is directly proportional to the potential difference across its ends (1)

2.6 The work done in moving a unit charge from one point to another in an electric field (1)

[6]

QUESTION 3

The sketch below shows the components of a photocell used in a camera light meter.

[pic]

Inside the photocell is a substance with a low threshold frequency. When monochromatic red light from a 50 W light bulb strikes the caesium cathode in the photocell, the meter gives a reading.

The 50 W bulb is then replaced with a 100 W bulb. The meter now gives a different reading.

3.1 What is the name given to the phenomenon described? (1)

3.2 What will the effect on the current be? Answer “increases”, “decreases” or “remains the same”. (1)

3.3 What is the proportional effect of the change in power of the light bulb on the magnitude of the current? (1)

3.4 Explain your answer in 3.3 (2)

3.5 Give another application of the phenomenon identified in 3.1 (1)

The wavelength of the red light in the 100 W bulb is 600 nm.

3.6 Calculate the energy of the incident photon. (6)

3.7 What is meant by the work function of the caesium cathode? (2)

3.8 Determine the speed of the photoelectrons if the work function of the metal is 2,8x10–19. (6)

[20]

QUESTION 4

Consider the sketch below illustrating the consecutive paths of a single source of light, first through a single slit, and then through a double slit.

[pic]

Light diffracts through each slit.

4.1 What is observed when light passes through the double slit? Give a reason for your answer. (4)

4.2 Describe how the pattern changes when the distance between the double slits is made smaller. (2)

Xoliswa claims that the same result could be obtained if two light sources are used with a double slit, as shown in the diagram below:

[pic]

4.3 Is Xoliswa’s idea feasible if one wishes to obtain the same results? Give a reason for your answer. (6)

[12]

QUESTION 5

Two unmarked test-tubes contain methyl ethanoate and propanoic acid at room temperature. Both solutions are colourless.

5.1 Give the structural formula for:

(a) methyl ethanoate (3)

(b) propanoic acid. (3)

5.2 Explain why methyl ethanoate and propanoic acid can be regarded as isomers of each other. (2)

5.3 Which solution would have a pleasant smell? Justify your answer. (2)

5.4 How can one distinguish between the two solutions using a simple chemical test? (2)

[12]

QUESTION 6

In the last four decades it has become cheaper to manufacture ethanol for industrial use from petroleum by-products, specifically by the addition of water to ethylene using a catalyst at high temperature and high pressure.

6.1 Give a balanced equation using structural formulae showing the formation of ethanol from ethylene and steam. (3)

6.2 Ethanol is the “alcohol” of alcoholic beverages. A dilute solution of ethanol is present in beer and wines. Describe how this method of preparation is different to the method in 6.1. Support your answer with a balanced chemical equation. (3)

6.3 Propan-2-ol is the alcohol commonly found in rubbing alcohol used by doctors and nurses. Write down the name and structural formula of an isomer of propan-2-ol. (3)

6.4 What is the IUPAC name of glycerol, the alcohol commonly used as a softener in soaps and lotions? (2)

6.5 What is the name of the organic compound formed when ethanol, in an acidified solution of potassium dichromate, is carefully heated? (2)

[13]

QUESTION 7

The following circuit diagram consists of a number of resistors that are connected to a 6 V battery.

[pic]

7.1 State Ohm’s law in words. (3)

7.2 Calculate the potential difference across the parallel combination of resistors. (1)

7.3 Calculate the reading on ammeter A2. (6)

7.4 Calculate the resistance of resistor R2. (3)

[13]

Total [[90]]

QUESTION 4

In the following diagram, the cloud is 400 m above the ground. A uniform electric field of

8 500 N(C-1 exists between the cloud and the ground.

[pic]

4.1 Calculate the potential difference between the cloud and the ground. (4)

4.2 The base of the cloud has a surface area of 1,4 km2. Calculate the capacitance between the cloud and the ground. Assume that the dielectric constant for air is the same as that of a vacuum. (4)

4.3 Calculate the charge that is accumulated at the base of the cloud. (3)

[11]

[TOTAL: 92 marks]

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