4 years ago

An electric kettle. The input energy is 10 Joules. The useful output energy is heat 9

Physics

1 answer:

mina [271]4 years ago

3 0

Answer:

Efficiency = 90 %

Wasted energy = 10 %

Explanation:

Since we have the input energy and useful output energy of the electric kettle, the only thing we are required to calculate here is its efficiency. This is gotten from

E = useful output energy/input energy × 100

E = 9/10 × 100 = 90 %

The percentage of wasted energy is

W = wasted energy/input energy × 100

W = 1/10 × 100

W = 10 %

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The temperature of a solution will be estimated by taking n independent readings and averaging them. Each reading is unbiased, w

Viktor [21]

Answer:

68 readings.

Explanation:

We need to take this problem as a statistic problem where the normal distribution table help us.

We can start considerating that X is the temperature of the solution, then

$0.9 = P(|\bar{x}-\mu|$

$0.9 = P(\frac{|\bar{x}-\mu|}{\frac{\sigma}{\sqrt{n}}}$

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For a confidence level of 90% our $Z_{critic}$ is 1.645

Therefore,

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Substituting for $\sigma = 5$ and re-arrange for n, we have that n is equal to

$n=(\frac{1.645\sigma}{0.1})^2$

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We need to make 68 readings for have a probability of 90% and our average is within $0.1\°\frac$

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