### Video Transcript

The figure shows a thermometer that
has been left outside in the shade on a hot day. What temperature reading does the
thermometer give to the nearest degree?

We can see that we’ve been given
this figure that shows a thermometer, which is a device that can be used to measure
temperature. We can notice that at the bottom of
this thermometer there’s a reservoir or bulb that’s filled with something red. And this red substance then extends
some way up the scale of the thermometer. This red substance is a liquid that
expands when its temperature increases.

Now this liquid expands with
temperature in a known and predictable way. So, depending on the temperature of
this bulb, the liquid in it will expand a certain amount. And as a result of this expansion,
it will rise up the tube in the thermometer. The amount that it expands
determines the height that the liquid rises to. And so, the height of the liquid in
the thermometer tube indicates the temperature.

We can notice that we’ve got a
scale drawn on the side of this thermometer. There are big marks on the scale of
five-degree increments. And these marks are labeled with
numbers. Then between each of these big
marks, there are four of these smaller marks. Since these four small marks
separate this five-degree region into one, two, three, four, five smaller regions,
then we know that each one of these small marks corresponds to one degree.

We also need to take some care over
the particular temperature scale that’s being used here. We can recall that there are
several different temperature scales, including the Fahrenheit, the Celsius, and the
Kelvin scale. Looking at the top of the
thermometer, we can see that we’ve got this degree C written on it. The C here stands for Celsius, and
it tells us that this thermometer measures temperature on the Celsius scale. That means that a temperature
measured with this thermometer must have units of degrees Celsius. And so, each small mark on the
thermometer corresponds to one degree Celsius.

In order to read off the
temperature in units of degrees Celsius that this thermometer is measuring, we just
need to see how far up the temperature scale this red line comes. The line comes up to this point
here, which is actually partway between two marks on the temperature scale.

Let’s now have a closer look at
what’s going on in this region of the thermometer. Looking now at this zoomed-in view,
we can see more clearly the height that the liquid rises to. That height is above this small
mark, which is two small marks below the 30-degree Celsius mark, and below this
small mark, which is one mark below 30 degrees Celsius.

Since we know that each small mark
corresponds to one degree Celsius, then we know that the upper small mark, which is
one mark below 30 degrees Celsius, must be 29 degrees Celsius and the one below
this, the lower mark, must be 28 degrees Celsius. Since the liquid reaches a height
in the tube that’s between these two small marks, then we know that this thermometer
is measuring a temperature that’s between 28 degrees Celsius and 29 degrees
Celsius. And since the thermometer scale
only has marks at one-degree increments, then the resolution of this thermometer is
not great enough to give an answer to more precision than this. That’s okay though because the
question is asking us for the temperature reading given to the nearest degree.

If we look closely at the height of
the liquid in this tube, we can notice that it’s ever so slightly closer to the mark
above it at 29 degrees Celsius than it is to the mark below it at 28 degrees
Celsius. That means that the temperature
being measured by this thermometer must be slightly closer to 29 degrees Celsius
than it is to 28 degrees Celsius. This means that our answer is then
that, to the nearest degree, the temperature reading given by this thermometer is
equal to 29 degrees Celsius.