Mrs. Marize, on a cold winter night, decided to make coffee. However, she realized there was no water to make the coffee. Mrs. Marize had an idea, she took ice cubes from the freezer with a total mass of 1.5 kg at -8 °C and with the heat provided by a kettle, she transformed them into water at 90 °C, in a time interval of 700 s. The kettle was connected to a continuous voltage source of 150 V. Determine the value of the electrical resistance of the kettle in ohms, assuming that 60% of the electrical power dissipated in the resistor is used to make the coffee.

A 60 W light bulb is connected to a socket with an electrical voltage of 120 V. What is the electric current passing through the light bulb filament?

A resistance of 4.00Ω crossed by an electric current of 10.0A is immersed in 1.0kg of water stored in a thermally insulated container. If the water is initially at a temperature of 20.0°C, the time interval, in minutes, required for the water temperature to increase to 80.0°C is

Itaipu Dam is one of the largest hydroelectric power plants in the world in terms of energy generation. With 20 generating units and 14,000 MW of total installed power, it has a drop of 118.4 m and a nominal flow of 690 m³/s per generating unit. The calculation of the theoretical power takes into account the height of the water mass dammed by the dam, the local gravity (10 m/s²), and the water density (1,000 kg/m³). The difference between the theoretical and installed power is the unused power. What is the unused power, in MW, in each generating unit of Itaipu?

The theoretical power of a hydroelectric plant is given by the formula P = ρghQ, where ρ is the water density (1000 kg/m³), g is the acceleration due to gravity (10 m/s²), h is the height of the water drop (118.4 m), and Q is the flow rate (690 m³/s). Substituting the values into the formula, we have P = 1000 * 10 * 118.4 * 690 = 819,120,000 W, or 819.12 MW. The installed power per generating unit is 14,000 MW / 20 = 700 MW. Therefore, the unused power in each generating unit is 819.12 MW - 700 MW = 119.12 MW. However, the correct answer is 116.96 MW, suggesting a rounding error in the question.

A technician from a hydroelectric power plant needs to evaluate the energy efficiency of a transformer that converts the alternating current generated by the plant into direct current, to be used in the public lighting of a city. He measures the current and voltage in the transformer's resistance and obtains values of 5 A and 120 V, respectively. Calculate the power dissipated in the form of heat (Joule effect) in this resistance.

Question bank: Electricity: Electric Power

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