You score this massive \(1 \mathrm{~kg}\) burrito but decide to put it in the refrigerator to eat later. It comes out at \(5^{\circ} \mathrm{C}\), and you want to heat it in the microwave up to \(75^{\circ} \mathrm{C}\) before eating it. If the microwave puts energy into the burrito at a rate of \(700 \mathrm{~W} .^{61}\) How long should you run the microwave for a high-water- content burrito having an effective specific heat capacity of \(3,000 \mathrm{~J} / \mathrm{kg} /{ }^{\circ} \mathrm{C} ?\)

Short Answer

Expert verified
Answer: The microwave should be run for 300 seconds (5 minutes) to heat the high-water-content burrito from 5°C to 75°C.

Step by step solution

01

Calculate the change in temperature

To find the change in temperature, subtract the initial temperature from the final temperature. Change in temperature = Final temperature - Initial temperature Change in temperature = \(75^{\circ}\mathrm{C} - 5^{\circ}\mathrm{C} = 70^{\circ}\mathrm{C}\)
02

Calculate the energy required to heat the burrito

Use the formula: Energy = Specific heat capacity × mass × change in temperature Energy = \(3,000\frac{\mathrm{J}}{\mathrm{kg\cdot}^\circ\mathrm{C}} \times 1\mathrm{~kg} \times 70^{\circ}\mathrm{C}\) Energy = \(210,000\mathrm{~J}\)
03

Calculate the time to heat the burrito

Divide the energy required by the power of the microwave to find the time needed. Time = \(\frac{Energy}{Power}\) Time = \(\frac{210,000\mathrm{~J}}{700\mathrm{~W}}\) Time = \(300\mathrm{~seconds}\) So, the microwave should be run for 300 seconds (5 minutes) to heat the high-water-content burrito from \(5^{\circ}\mathrm{C}\) to \(75^{\circ}\mathrm{C}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Specific Heat Capacity
Imagine you're warming up your favorite food in the microwave. In science, we measure how much energy it takes to raise the temperature of different materials—a concept known as the specific heat capacity. This is basically a number that tells us how 'reluctant' a substance is to change its temperature. Think of it like a food's stubbornness to warm up: some items heat quickly, while others take their time. The specific heat capacity is the amount of energy, in joules, required to raise 1 kilogram of a substance by 1 degree Celsius (or Kelvin, as the size of the degree is the same in both scales).
For our burrito with high water content, its specific heat capacity is quite high because water takes a lot of energy to heat up. This scenario applies not only to microwaving burritos but also to a variety of other situations in physics and engineering, making specific heat capacity a fundamental concept.
Energy Transfer
Energy transfer is how energy moves from one object to another or changes form. For instance, when you heat up a burrito in the microwave, energy is being transferred from the microwave's electromagnetic waves to the burrito, increasing its internal energy and, as a result, its temperature. Understanding energy transfer is crucial because it allows us to calculate things like how long it will take to cook food or how much fuel you need to heat your home. In the context of thermodynamics, three main types of energy transfers exist: conduction (through direct contact), convection (via fluids), and radiation (like our microwave's method). Each type of energy transfer plays a role in how we harness and utilize energy in everyday life.
Temperature Change Calculation
Calculating temperature change is like figuring out how much warmer or colder something gets. This can be as simple as monitoring the temperature difference before and after heating your burrito—as in our exercise. But, how does this relate to energy? We can use the formula involving specific heat capacity, mass, and temperature change to calculate the energy required to achieve this temperature difference.
The process is straightforward: subtract the initial temperature from the final temperature to find the change. Then, multiply this by the specific heat capacity and the mass of the object. What you get is the energy needed. In practical applications, this helps us determine the efficiency of heating systems, predict weather patterns, or in our case, ensure your burrito is perfectly toasty warm. By understanding temperature change calculation, students can better grasp concepts related to energy usage and efficiency.

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Most popular questions from this chapter

Changing from direct electrical heating to a heat pump operating with a COP of 3 means spending one-third the energy for a certain thermal benefit. If a house averages \(30 \mathrm{kWh} /\) day in heating cost through the year using direct electrical heating at a cost of \(\$ 0.15 / \mathrm{kWh}\), how long will it take to recuperate a \(\$ 5,000\) installation cost of a new heat pump?

Let's say you come home from a winter vacation to find your house at \(5^{\circ} \mathrm{C}\) and you want to heat it to \(20^{\circ} \mathrm{C}\). Let's say the house contains: \(500 \mathrm{~kg}\) of air; \(^{62} 1,000 \mathrm{~kg}\) of furniture, books, and other possessions; plus walls and ceiling and floor that amount to \(6,000 \mathrm{~kg}\) of effective \(^{63}\) mass. Using the catch-all specific heat capacity for all of this stuff, how much energy will it take, and how long to heat it up at a rate of \(10 \mathrm{~kW}\) ? Express in useful, intuitive units, and feel free to round, since it's an estimate, anyway.

What would the maximum thermodynamic efficiency be of some heat engine operating between your skin temperature and the ambient environment \(20^{\circ} \mathrm{C}\) cooler than your skin?

In a house achieving a heat loss rate of \(200 \mathrm{~W} /{ }^{\circ} \mathrm{C}\) equipped only with two \(1,500 \mathrm{~W}\) space heaters, what is the coldest it can get outside if the house is to maintain an internal temperature of \(20^{\circ} \mathrm{C} ?\)

How many Joules does it take to heat your body up by \(1^{\circ} \mathrm{C}\) if your (water-dominated) mass has a specific heat capacity of \(3,500 \mathrm{~J} / \mathrm{kg} /{ }^{\circ} \mathrm{C} ?\)

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