# Physical Science Question on Electrical Power and Energy

• CEF721
In summary, the electric space heater uses 1800 watts of power and costs $18 to operate for 30 days. For the second question, a family of four would use 48,000 kWh of electricity a year and this would require 60,000 kg of coal to be burned (assuming 40% efficiency). This would result in a pile of coal with a volume of approximately 23 cubic meters and would release approximately 1.98 x 109 joules of heat to the environment. CEF721 1. An electric space heater draws 15.0 A from a 120 V source. It is operated, on average, for 5.0h (hours) each day. a) How much power does the heater use and b) At$.10 per kWh, what does it cost to operate the heater for 30 days?
2. Suppose each person in the United States uses 12,000 kWh of electricity a year and the power plants using coal to generate electricity are 40% efficient. If 1.0 kg of burned coal releases 33.0 mJ a) how much coal will be burned during a year for a family of four b) how large a pile of coal would that be (using 2620 kg/ m^3) c) how much heat is given off to the environment

power= current x voltage, energy= power x time

I can find a) at 1800 w (watts), but I have no idea where to start on part b.
For 2, I'm unsure of where to star. I know the family of four would use 48,000 kWh a year, but after that, I'm lost

CEF721 said:
1. An electric space heater draws 15.0 A from a 120 V source. It is operated, on average, for 5.0h (hours) each day. a) How much power does the heater use and b) At \$.10 per kWh, what does it cost to operate the heater for 30 days?
2. Suppose each person in the United States uses 12,000 kWh of electricity a year and the power plants using coal to generate electricity are 40% efficient. If 1.0 kg of burned coal releases 33.0 mJ a) how much coal will be burned during a year for a family of four b) how large a pile of coal would that be (using 2620 kg/ m^3) c) how much heat is given off to the environment

power= current x voltage, energy= power x time

I can find a) at 1800 w (watts), but I have no idea where to start on part b.
For 2, I'm unsure of where to star. I know the family of four would use 48,000 kWh a year, but after that, I'm lost

A kWh is the energy equivalent to one kilowatt for one hour duration. As you may recall, a Watt is equivalent to a Joule per second (J/s). So a kWh is 1000 W x 1hr = 3.6 x 106 J.

For the first question you should be able to work out how many hours the heater runs in the 30 day period, and then find the kWh, etc.

## 1. What is electrical power and energy?

Electrical power is the rate at which electrical energy is transferred or converted into other forms of energy. Electrical energy is the energy that is carried by an electric current and can produce useful work.

## 2. How is electrical power measured?

Electrical power is measured in watts (W), which is equal to one joule of energy per second. Kilowatts (kW) and megawatts (MW) are commonly used to measure larger amounts of power.

## 3. What is the difference between AC and DC power?

AC (alternating current) power is the type of electrical power that is commonly used in homes and businesses. It continuously changes direction and is delivered through power lines. DC (direct current) power flows in one direction and is commonly used in electronic devices such as batteries.

## 4. How is electrical energy generated?

Electrical energy is generated by converting other forms of energy such as chemical, thermal, or mechanical energy into electrical energy. This is typically done through power plants using generators.

## 5. How can we conserve electrical energy?

There are several ways to conserve electrical energy, including using energy-efficient appliances, turning off lights and electronics when not in use, and using alternative sources of energy such as solar or wind power. It is also important to reduce energy waste by properly insulating homes and buildings.

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