7. 10 Kg of water at 90°C is cooled by mixing 20kg of water at 20°C. What is the final temperature of the mixture?
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object 2 because all the other ones are wrong

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.

radiation

explanation:

heat is transmitted by radiation