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1 answer:
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Answer:
5 ohms
Explanation:
Given:
EMF of the ideal battery (E) = 60 V
Voltage across the terminals of the battery (V) = 40 V
Current across the terminals (I) = 4 A
Let the internal resistance be 'r'.
Now, we know that, the voltage drop in the battery is given as:
Therefore, the voltage across the terminals of the battery is given as:
Now, rewriting in terms of 'r', we get:
Plug in the given values and solve for 'r'. This gives,
Therefore, the internal resistance of the battery is 5 ohms.
First of all, we need to write the First Law of thermodynamics assigning the correct sign convention:
where
is the change in internal energy of the system
Q is the heat absorbed/released
W is the work done
and the signs are assigned based on whether there is an increase in the internal energy or not. Therefore:
Q is positive if it is absorbed by the system (because internal energy increases)
Q is negative if it is released by the system (because internal energy decreases)
W is negative if it is done by the system on the surrounding (because internal energy decreases)
W is positive if it is done by the surrounding on the system (because internal energy increases)
Using these definitions, we can now fill the text of the question:
When a system is heated, heat is ABSORBED by the system. The amount of heat added is given a POSITIVE sign. When a system is cooled, heat is RELEASED by the system. The amount of heat is given a NEGATIVE sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done BY the system and is given a NEGATIVE sign. If a gas is compressed, then work is done ON the system. This work is given a POSITIVE sign.