BLE Model Paper 4

A computer-made, three-dimensional world that a person can look around and act in, as if really there, using equipment such as a headset, headphones and motion sensors.

Cloud computing: the files are kept on remote servers in data centers (for example Google Drive or OneDrive) and reached over the internet from any device.

Because they come from one parent only, with no fusion of male and female gametes, so they get exactly the same genes as the parent (they are clones).

No. Velocity has a direction as well as a size. The tip goes round in a circle, so its direction changes all the time, and its velocity changes too, though its speed stays the same.

The angle between the geographic meridian and the magnetic meridian at a place.

Because electrons are so light (one electron is only about 1/1836 of the mass of a proton) that they make almost no difference. Nearly all the mass of an atom is in its nucleus, its protons and neutrons.

He changed a formula instead of putting a number in front of it. H₂O₂ is not water (it is a different substance), so the equation no longer describes the reaction. Only the coefficients may change:
$$2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$$
(Check: 4 H and 2 O on each side.)

Yes. Ordinary rain has a pH of about 5.6; rain with a pH below 5.6 is acid rain. The smoke of the kilns, which burn coal, puts oxides of sulphur and nitrogen into the air, and they form acids in the rain.

• i.Factory passwords are the same on many devices and are easy for hackers to find. A router still using one can be taken over by malware and made part of a botnet, as hundreds of thousands of cameras and routers were in the Mirai attack of 2016.
• ii.Updates fix the weaknesses that attackers already know about, so an up-to-date computer is much harder to break into with malware.

No, I don’t agree.

• a.A national park is large, so poaching is hard for its staff alone to control. Villagers who live beside it can notice strangers and traps and tell the park at once.
• b.The villagers gain from the park: people in the buffer zone share in its income, and its wildlife brings ecotourism, food and livelihoods. Protecting biodiversity is also every citizen’s duty, not only the government’s.

• i.Food made in the leaves travels down the stem in the phloem, just under the bark. Peeling the ring cuts the phloem, so food (and the plant’s rooting hormone) piles up just above the cut, and roots grow there. The xylem in the wood is not cut, so water still reaches the leaves.
• ii.Sealing keeps out air, water and germs, so the cut surfaces don’t dry out or get infected while the stock and the scion grow together into one plant.

i. $u$ = 24 m/s, $v$ = 0, $t$ = 6 s.
$$a = \frac{v - u}{t} = \frac{0 - 24}{6} = -4\ \text{m/s}^2$$
The acceleration is −4 m/s², so the retardation is 4 m/s².
ii. It slows down steadily, so its average velocity is
$$\bar v = \frac{u + v}{2} = \frac{24 + 0}{2} = 12\ \text{m/s}, \qquad s = \bar v \times t = 12 \times 6 = 72\ \text{m}$$

• i.Any two: it makes it hard to concentrate on reading and writing, so the students learn more slowly; it causes headaches and stress; over a long time, loud noise weakens hearing; it raises blood pressure.
• ii.Any two: plant rows of trees between the road and the school (leaves and branches absorb and scatter sound); put up “no horn” signs near the school and ask drivers not to use the horn without need; ask that vehicles be fitted with silencers and kept in good order; use the rooms on the far side of the building for teaching.

• i.Overloading: together the three appliances draw more current than the circuit is made for. The thin fuse wire, of low melting point, heats up and melts, breaking the circuit before the wiring is damaged.
• ii.A thick copper wire won’t melt, so the protection is gone. The next time too much current flows, the house wiring itself heats up, which can damage the appliances and start a fire inside the walls. (The fuse must be replaced with one of the same rating, and fewer appliances used at once.)

• i.A group is a vertical column of the table, of elements with similar properties; a period is a horizontal row, along which the properties change step by step.
• ii.18 groups and 7 periods.

• i.They all formed from one flat, spinning disc of gas and dust around the young Sun, so they kept its plane and its direction of turning.
• ii.Gas torn out of the Sun would be millions of degrees hot, so it would spread out into space instead of clumping into planets. Close passes between stars are also extremely rare.

• i.The temperature of the water (hot or cold): that is what she is testing.
• ii.Any two: the amounts of water were different (100 mL and 200 mL); the sugar was in different forms (powder and a cube); she stirred only the hot water.
• iii.Take the same amount of water in two identical beakers, one hot and one cold; add the same amount of the same sugar (both powdered) to each; stir both in the same way (or neither); and time how long each takes to dissolve. Repeating the test makes the result more reliable.
• iv.Step 4. The rule: never taste anything in a laboratory (a beaker or rod may carry traces of chemicals). She should watch for the sugar to disappear instead.

Her conclusion may well be true, but her test can’t show it: the powder and the stirring alone could have made the sugar in the hot water dissolve faster.

• i.The onion skin is thin and see-through, so its cells are hard to see. Safranin is a stain: it colors the cell walls and the nucleus, so the parts of the cells show up clearly.
• ii.To remove the extra stain. Too much stain would color everything dark, and the parts of the cells couldn’t be told apart.
• iii.So that no air bubbles are trapped under it. Lowered slowly from one edge, the liquid spreads ahead of the cover slip and pushes the air out; a bubble would spoil the view.

iv. Onion scales grow underground, away from light, so they don’t make food by photosynthesis and have no chloroplasts.

• i.$R = 2f = 2 \times 15 = 30\ \text{cm}$. C is 30 cm and F is 15 cm in front of the mirror, so the candle, at 40 cm, is beyond C.
• ii.A ray from the top of the flame parallel to the principal axis is reflected through F; a ray through C comes back along itself. Where they cross is the top of the image.

• iii.The image is between F and C (in front of the mirror, about 24 cm from it). It is real, inverted and diminished.
• iv.At 10 cm the candle is between F and P. The reflected rays spread out and never actually meet, so no real image forms that could be caught on a screen. They only seem to meet behind the mirror, where a virtual, erect and magnified image forms.

• i.Boiling didn’t remove the hardness, so it is permanent hardness, caused by the sulphates and chlorides of calcium and magnesium (such as calcium sulphate and magnesium chloride).
• ii.Layers of gravel, coarse sand and sodium zeolite. As the hard water trickles down through the zeolite, the calcium and magnesium ions in the water swap places with the sodium ions of the zeolite; the sodium ions don’t cause hardness, so soft water comes out at the bottom.

• iii.When the zeolite is full of calcium and magnesium, it is washed with strong salt (sodium chloride) solution, which puts the sodium back. It can then be used again and again.
• iv.Adding washing soda (sodium carbonate), which turns the dissolved salts into insoluble carbonates that are filtered off:

Calcium sulphate + sodium carbonate → calcium carbonate + sodium sulphate
$$\text{CaSO}_4 + \text{Na}_2\text{CO}_3 \rightarrow \text{CaCO}_3 + \text{Na}_2\text{SO}_4$$