New Scientist - UK (2022-06-11)

11 June 2022 | New Scientist | 55

Answers

Quick quiz #155

Answers

1 Halley’s comet

2 James Lind

3 The testicles

4 They are carnivorous

5 Phylum

Quick crossword

#109 Answers

ACROSS 1 Rattus, 5 Codify,

10  Lignite, 11 Fifteen,

12  Cobalt,  15 Brazil, 16 Ergo

sum, 17  Lead,  18 Iron, 19 Acrylic,

20  Pike, 22  Itch, 25 Aerobic,

27  Saliva, 28 Albino, 31 Orbiter,

32  Amniote, 33 Stereo, 34 Fossil

DOWN 2 Algebra, 3 Triple,

4  Stem, 5 Cuff, 6 Deform,

7  Freezer, 8 Glycol, 9 Inulin,

13  Trachea, 14 Polygon,

15  Bulimia, 20 Piston, 21 Kilobit,

23 Tripoli, 24 Hoover, 25 Avatar,

26 Clones, 29 Argo, 30 Half

#170 Presents,

but not correct

Solution

Amelia – lip balm; Beth –

sunglasses; Clara – book; Diaz –

nail varnish; Elinor – pencils.

Kayleigh scores better with

each guess, so at least two

of her third guesses are right.

Clara can only be nail varnish

or book, and since at least one

of the second guesses is correct,

it quickly emerges that only two

of the third guesses can be right:

that Amelia gave lip balm and

Beth gave sunglasses.

The rest follows.

Tom Gauld

for New Scientist

droplets. Steam, a gas, is invisible.
What is happening is that the
heated pan is producing the
invisible steam; taking it off the
hob allows cooling, so the visible
water droplets condense out.

Hazel Russman
London, UK
With a boiling kettle, where you
have water vapour coming out of
a fairly narrow spout, steam often
first appears at some distance
from the edge of the spout, due
to the cooling off of the vapour.

David Muir
Edinburgh, UK
The amount of invisible water
vapour that air can hold depends
on temperature. The lower the air
temperature, the less water vapour
can remain in the gas phase. If the
air temperature falls, there will
come a point, the dew point, when
the air is fully saturated with water
vapour. When the temperature
drops further, water vapour
condenses into the tiny droplets
we observe as mist/cloud/steam,
depending on where it forms.

If you have a gas hob, you

can switch the gas off and on

every few seconds and watch the

steam appear then disappear. This

can be confirmed by holding a

thermometer several centimetres

over heated water and removing

the pot from the hob or switching

the gas off. A drop of 5°C is almost

immediate with the appearance of

steam, released from the air, not

from the water as suggested by

the questioner.

Tim Jackson

Haslingden, Lancashire, UK

In my experience, the steam cloud

seen when moving a pan off the

hob, or turning off the gas, isn’t an

increase in steam released, but a

disturbance of the convection

plume over the pan making

the steam more visible.

While the pan is in a steady

state, the plume flowing from it is

fairly smooth, with regular layers,

and the water vapour remains hot

and transparent until it condenses

on a cool surface or gets drawn

into an extractor.

When the flow is disturbed, it

becomes turbulent and mixes

with cold air causing a cloud

of droplets to condense out.

Likewise, if you lift the lid off a

simmering pan, the pan quickly

fills with a steam cloud.

Sam Edge

Ringwood, Hampshire, UK

I suspect that the act of moving

the pan causes turbulence in

super-critical zones – where the

water is still liquid, but slightly

above the boiling point

temperature.

This provides enough extra

energy to change the water’s phase

from liquid to gas. It may also

move the water from relatively

smooth parts of the pan’s surface

to ones with microscopic flaws

that provide seed points for the

growth of bubbles. ❚

“ If cooking on a gas

hob, you can switch

the gas off and on

every few seconds and

watch steam appear

then disappear”