Electromagnets have certain advantages over permanent magnets. One of the major advantage is, the amount of electric current can easily be controlled, in turn, magnetic field can be controlled. Out of all the options, option D would be the best answer.
In short, Your Answer would be option D) Electromagnets can easily be turned on and off.
Hope this helps!
Before going to solve this question first we have to understand specific heat capacity of a substance .
The specific heat of a substance is defined as amount of heat required to raise the temperature of 1 gram of substance through one degree Celsius. Let us consider a substance whose mass is m.Let Q amount of heat is given to it as a result of which its temperature is raised from T to T'.
Hence specific heat of a substance is calculated as-
![c= \frac{Q}{m[T'-T]}](https://tex.z-dn.net/?f=c%3D%20%5Cfrac%7BQ%7D%7Bm%5BT%27-T%5D%7D)
Here c is the specific heat capacity.
The substance whose specific heat capacity is more will take more time to be heated up to a certain temperature as compared to a substance having low specific heat which is to be heated up to the same temperature.
As per the question John is experimenting on sand and water.Between sand and water,water has the specific heat 1 cal/gram per degree centigrade which is larger as compared to sand.Hence sand will be heated faster as compared to water.The substance which is heated faster will also cools faster.
From this experiment John concludes that water has more specific heat as compared to sand.
Answer:
empty
Explanation:
Nutritionists call the calories found in junk food empty calories due to lack of quality nutrients.
Empty calories refer to calories derived from foods containing no quality nutrients. These foods are mainly junk food; food that contains high calories derived from fat or sugars and with little or no proteins, fiber, dietary minerals or vitamins. These foods are not healthy as their prolonged consumption can lead to an increased risk of obesity.
Answer:
P = 5280 W
Explanation:
The conductivity of the materials determines that heat flows from the hot part to the cold part, the equation for thermal conductivity transfer is
P = Q / t = k A (
-
) / L
Where k is the thermal conductivity of the glass 0.8 W / ºC, A the area of the window, T the temperature and L is glass thickness
Let's calculate the window area
A = l * a
A = 2.0 1.0
A = 2.0 m²
Let's replace
L = 0.5 cm (1 m / 100 cm) = 0.005 m
P = 0.8 2 (20.5 - 4) / 0.005
P = 5280 W