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An electrical heater at 80 °C warms room air at 24 °C. Which description combines the energy form and transfer direction?
Thermal energy transfers from the cooler air to the hotter heater. Electrical energy becomes mainly thermal energy, which transfers from the hotter heater to the cooler air. Cold energy flows from the air into the heater and becomes electrical energy. Power is stored in the heater as a separate energy form. Which conversion sequence occurs in a fossil-fuel power station?
Chemical potential → thermal → kinetic → electrical energy. Electrical energy → chemical potential energy → thermal energy, without a turbine. Chemical potential energy in fuel → electrical energy directly in the boiler. The generator creates electrical energy without an input. Why is electrical energy transmitted across long distances at high voltage?
High voltage makes electricity move through the cable faster. High voltage produces a larger current, which cools the cable. High voltage creates replacement energy for cable losses. For the same power, high voltage allows a smaller current and therefore less cable heating. Which sequence correctly shows the transformers around a long-distance grid link?
Step-up at both ends because each transformer creates energy. Step-down at both ends so electricity travels faster. Step-up near the power station, then step-down near consumers. Step-down near the power station, then step-up near consumers. A battery toy receives 480 J in 40 s and ends with no stored-energy change. Records show 300 J as movement and 120 J as heating and sound. Which audit is correct?
The input power is 12 W and 60 J of output is unaccounted for because the listed transfers total 420 J. The input power is 19 200 W because energy and time must be multiplied. The energy account is complete because useful movement may be less than the input. The record creates 60 J because the listed output exceeds the input.
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A book is lifted from the floor onto a shelf and comes to rest. Which energy form has increased?
Gravitational potential energy. Kinetic energy, because the book is still moving on the shelf. Sound energy, because height is a kind of sound. Power, because the shelf stores the lifting rate. An ice pack at 0 °C is left in a room at 25 °C. Which transfer statement is correct before equilibrium?
Net thermal energy transfers from the room to the ice pack. Net thermal energy transfers from the ice pack to the warmer room. Cold energy leaves the ice pack and enters the room. No net transfer can occur while the temperatures differ. A ball loses kinetic energy as it rolls to rest. What does conservation of energy require?
Every energy form must stay at the same amount. Only energy that keeps the ball moving needs to be counted. Energy is transferred to other forms and the surroundings, including thermal and sound energy. The kinetic energy ceases to exist. What is the turbine's role in a fossil-fuel power station?
It burns the fuel and sends electricity into the boiler. It creates energy to replace thermal transfers. It cools the steam but does not connect to the generator. Steam turns it, and the rotating turbine drives the generator. What unwanted energy transfer occurs when current passes through a transmission cable with resistance?
A larger current removes thermal energy from the cable. Energy is transferred to the cable and surroundings by heating. Energy is destroyed inside the cable. Electrical energy becomes trapped without warming the cable. An AC device requires a higher operating voltage than a suitable AC supply provides. Assume a correctly rated transformer is available. Which transformer role is needed?
A step-up transformer raises the supply voltage to the required value. A step-down transformer, because it raises voltage. The same transformer direction as every other appliance. No input source, because a step-up transformer creates energy. A 60 W lamp operates for 5 minutes and a 20 W lamp operates for 20 minutes. Which comparison of their electrical energy transfers is correct?
The 20 W lamp transfers more energy: 24 000 J compared with 18 000 J for the 60 W lamp. The 60 W lamp transfers three times as much energy because its power is three times greater. Both lamps transfer the same energy because power and time cancel automatically. The 20 W lamp transfers 400 J and the 60 W lamp transfers 300 J because minutes may be used directly with watts.
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A cart rolls across a level floor. Which energy form is associated with its motion?
Power, because motion is itself a stored power form. Kinetic energy. Gravitational potential energy only, because all moving objects are raised. Elastic potential energy, although nothing is stretched or compressed. A metal spoon at 20 °C is placed in tea at 70 °C. Before equilibrium, what is the direction of net thermal-energy transfer?
There is no transfer until both reach the same temperature. From the hotter tea to the cooler spoon. From the cooler spoon to the hotter tea. Cold energy flows from the spoon into the tea. A lamp receives 100 J and transfers 15 J as light. Which complete account is consistent with conservation?
Every joule must remain as electrical energy. The other 85 J is transferred, mainly as thermal energy. Only the useful 15 J is conserved. The other 85 J has been destroyed. Two machines each transfer 1200 J. Machine X takes 20 s and machine Y takes 40 s. Which is more powerful?
They have equal power because their energies are equal. Neither, because power is measured in joules. Machine X; it transfers the same energy in less time. Machine Y, because a longer time means greater power. Which ordered energy-conversion chain begins with fossil fuel and ends with electricity?
Electrical → kinetic → thermal → chemical potential. Chemical potential → electrical directly inside the boiler. No input chain is needed because the generator creates energy. Chemical potential → thermal → kinetic → electrical. Where must the grid voltage be raised to reduce heating along a long transmission line?
Before the long line, using a step-up transformer. Only after the long line, using a step-down transformer. Inside the cable, because the transformer creates replacement energy. Anywhere, because voltage changes only electricity speed. Which statement is consistent with conservation of energy in a real transformer?
A step-up transformer creates extra output energy. A step-down transformer destroys all input energy. Energy conservation applies only to step-down transformers. Output energy cannot exceed input energy, and some energy may become thermal energy.
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