Electrical power and energy consumption

A toaster connected to $230\ \text{V}$ has a current of $2\ \text{A}$ passing through it. Calculate its power in watts.

A cell phone charger operates at $5\ \text{V}$ and delivers a current of $2\ \text{A}$. What power does it supply to the phone?

Order these appliances from lowest to highest typical power: an oven ($2500\ \text{W}$), an LED light bulb ($10\ \text{W}$), a television ($100\ \text{W}$) and a hair dryer ($1500\ \text{W}$), as shown in the figure.

Which converts more electrical energy per second?

An electric heater of $1150\ \text{W}$ is connected to the $230\ \text{V}$ outlet. What current flows through it?

An oven rated at $2300\ \text{W}$ is connected to a $230\ \text{V}$ power supply.

1. a) What current flows through it?
2. b) The kitchen outlet and cable can withstand up to $16\ \text{A}$: is there a risk of overload using only the oven? Justify your answer.

On an electric bill, consumption appears in $\text{kWh}$. Is the kilowatt-hour a unit of power or of energy? Explain in your own words what consuming $1\ \text{kWh}$ means.

A light bulb of $100\ \text{W}$ remains turned on for $10\ \text{h}$.

1. a) How much energy does it consume, in watt-hours?
2. b) Express it in kilowatt-hours.

A fan rated at $50\ \text{W}$ is turned on for $4\ \text{h}$. How much energy does it consume? Express it in $\text{Wh}$ and in $\text{kWh}$.

A heater rated at $1200\ \text{W}$ is turned on for $2\ \text{h}$ a day during a month of $30$ days.

1. a) Express its power in kilowatts.
2. b) Calculate the energy it uses in the month, in $\text{kWh}$.
3. c) If the price is $0.20\ \text{\$/kWh}$, how much does this usage cost?

An LED lamp rated at $10\ \text{W}$ provides the same light as an old bulb rated at $60\ \text{W}$, and both are turned on for $5\ \text{h}$ a day.

1. a) Calculate the energy consumed by each one in a month of $30$ days, in $\text{kWh}$.
2. b) With $\text{kWh}$ at $0.20\ \text{\$/kWh}$, how much money is saved per month with the LED?

We leave the house for a whole day and accidentally leave a $100\ \text{W}$ lamp turned on for $10\ \text{h}$.

1. a) How many $\text{kWh}$ has it consumed?
2. b) How much money have we wasted, at $0.20\ \text{\$/kWh}$?

On the energy rating label of a refrigerator, a letter between A and G appears.

1. a) What does this letter indicate?
2. b) Which letter should be chosen to pay less on the electric bill? Why?

The label of a new refrigerator indicates a consumption of $150\ \text{kWh}$ per year, whereas the old one at home consumes $450\ \text{kWh}$ per year.

1. a) How many $\text{kWh}$ are saved each year with the new one?
2. b) How much money does this saving represent at $0.20\ \text{\$/kWh}$?

An old television consumes $300\ \text{kWh}$ per year and a new LED television consumes $100\ \text{kWh}$ per year. The new television costs $\$400$ and $\text{kWh}$ is priced at $0.20\ \text{\$/kWh}$.

1. a) How much money is saved each year with the new television?
2. b) How many years will it take for the savings to offset the cost of the television?
3. c) Do you think the replacement is worth it? Explain your answer using the data.

A ceramic cooktop rated at $2\ \text{kW}$ operates for $15\ \text{min}$.

1. a) Express this time in hours.
2. b) Calculate the energy consumed, in $\text{kWh}$.
3. c) How much does it cost at $0.20\ \text{\$/kWh}$?

At Sophia's house, the following are used every day: an oven rated at $2\ \text{kW}$ for $1\ \text{h}$, ten LED bulbs rated at $10\ \text{W}$ turned on for $5\ \text{h}$ and a refrigerator rated at $200\ \text{W}$ operating for $24\ \text{h}$.

1. a) Calculate the $\text{kWh}$ consumed by each appliance per day.
2. b) How many $\text{kWh}$ are consumed in total in a month of $30$ days?
3. c) How much is the bill for the month at $0.20\ \text{\$/kWh}$?

A home electrical system allows a maximum of $3450\ \text{W}$ at any one time; if this is exceeded, the circuit breaker trips and the power goes out. The mains supply is $230\ \text{V}$. The diagram compares the power rating of the appliances with that maximum.

1. a) What maximum current does the electrical system allow?
2. b) Can we use the oven ($2300\ \text{W}$) and the washing machine ($2000\ \text{W}$) at the same time? Justify your answer with numbers.
3. c) What about the oven together with the microwave ($1150\ \text{W}$)?