ShmoopTube

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And here’s your Shmoop du jour, brought to you by joules.

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They’re the diamond-standard unit of energy, resplendent in their timeless beauty. [Girl wearing jewels and boy cries]

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We hear they're sold at Kay.

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Okay, here’s our question:

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Equal masses of two substances, A and B, each absorb 50 joules of energy.

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If the temperature of A increases by 3 °C, and the temperature of B increases by 6 °C,

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which of the following statements is true?

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And here are our potential answers: These must be some creepy substances… [Gas appears]

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Absorbing all this energy like dementors swallowing your soul… somebody should cast a patronus [Dementor appears]

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charm, quick.

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What's that?

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Any object that increases in temperature is absorbing energy?

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Oh….maybe we overreacted a little bit.

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So to solve this problem, let’s take a look at this equation. [Finger points to equation]

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Here, Q is the amount of heat or energy transferred when a material changes temperature, m is

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the material’s mass, Cp is the heat capacity, and delta T is the change in

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temperature.

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We know from the problem statement that substances A and B have the same mass.

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They also both absorb the same amount of energy, 50 joules.

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That means the only factors that can differ between them are the change in temperature [Thermometer rising in temperature]

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and the heat capacity.

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So let’s write that out as an equation, which looks a little something like….this.

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And even though it looks complicated, you don't have to be Hermione Granger to solve

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this one.

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The problem tells us the temperature increase for substance A is 3 degrees Celsius, while [Finger points to temperature increase for substance A]

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the temperature increase for substance B is 6 degrees Celsius.

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If we reduce this equation and cancel out the units, we can see that the heat capacity

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of material A is twice the heat capacity of material B. And that just happens to be answer

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choice (A).

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Well done. [Girl pours potion]

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You know, if you went to Hogwarts, we’re pretty sure you’d be a Ravenclaw, you smarty

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pants.

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