Which one has less resistivity 60W or 100W

Tasks and solutions for the use of electricity in the household

Make the calculations so that anyone who hasn't done them can easily understand!

Protection of the circuits:
The individual circuits are protected from overload by built-in automatic circuit breakers. These machines interrupt the circuit when the current strength exceeds a certain value.
There are built-in machines up to 10 A, 16 A, 20 A, 25 A, and 35 A.

1. Change the following formulas:









The following information can be found on an electrical device:
U = 60 V I = 3.5 A
Calculate the power and resistance.

Result: The power is P = 210 W.
The resistance is R = 17.14 ohms

3. A current of 115 mA flows through a light bulb at an output of 25 W.
Calculate the stress.

Result: The voltage is U = 217 V.

4. A 750 W heating stove consumed 5 kWh of electricity.
How long was it on?

Result: The heating furnace was turned on for 6 hours 40 minutes.

5. Calculate the resistance of an iron with the following inscription: 800 W 230 V.
Note: First calculate the amperage.

Result: The current is 3.478 A, the resistance is R = 66.12 Ohm.

6. A circuit has a voltage of 230 V. The following are connected:
1 radio 70 W
2 light bulbs 100 W each
1 iron 1000 W
3 light bulbs 40 W each
1 television set 260 W
With which built-in machine must the circuit be protected?

Result: Total output: P = 1650 W Current: I = 7.2 A Fuse: 10 A automat.

7. There are four circuits built into a household:

First circuit (230 V):
5 incandescent lamps, 60 W each
3 incandescent lamps, 100 W each
1 heating oven 600 W
1 radio set 44 W
Second circuit (230 V): 1 washing machine 3.2 kW
Third circuit (230 V): 1 hot water tank 6 kW
Fourth circuit (230 V): 1 dishwasher 2.9 kW
Calculate which machines must be used to protect the individual circuits.

First circuit total power P = 1244 W.
First circuit I = 5.409 A6 A fuse
Second circuit I = 13.91 A 16 A fuse
Third circuit I = 26.087 A35 A fuse
Fourth circuit I = 12.609 A 16 A fuse

8. A housewife receives an automatic ironing machine with a power consumption of 2.2 kW. It is found that, in addition to this device, there are also a 100 W lamp, three 60 W lamps and a 80 W radio in the same circuit. The circuit is fused with 10 A at 230 V voltage.
Can all devices be switched on at the same time?

Result: total power P = 2560 W.
If all consumers are connected at the same time, 11.13 A flow, the circuit is overloaded.

Additional task for all of the following tasks: The electricity prices are constantly changing, use current prices and calculate the price increase!

9. A 25 W light bulb in a hallway is replaced by a 60 W light bulb. This is switched on for 4 ½ hours a day. For 1 kWh you have to pay 0.122 €.
How high are the additional costs per month?

Result: The additional monthly costs are € 0.58.

10. Electricity consumption - electricity costs:

a) Calculate the electricity consumption in kWh and the electricity costs of the following electrical items in one hour and in six hours.
100 W light bulb
40 W light bulb
Immersion heater 750 W
2.5 kW heater
200 W vacuum cleaner
6.3 kW electric stove
One kWh costs € 0.122 including VAT.
b) Determine how long each device can be switched on until 1 kWh is consumed.
c) In what time do the individual devices consume electricity worth € 1?

a) devicePower consumptionEnergy costs
1 H.6 hours1 H.6 hours
100 W light bulb0,100,600,01220,0732
40 W light bulb0,040,240,00490,0294
Immersion heater0,754,500,09150,5490
Heating stove2,5015,000,30501,8300
vacuum cleaner0,201,200,02440,1464
Electric stove6,3037,800,76864,6116
deviceb) duty cyclec) switch-on time
100 W incandescent lamp10 h81 h 58 min
40 W incandescent lamp25 h204 h 05 min
Immersion heater1 h 20 min10 h 56 min
Heating stove24 min3 h 17 min
vacuum cleaner5 h40 h 59 min
Electric stove9.5 min1 h 18 min

11. An electric heater has a connected load of 2.2 kW. 1 kWh costs € 0.13. How long can it be in operation until electricity has been consumed for € 5?

Result: The operating time is 17.48 hours or 17 hours 29 minutes.

12. In the morning the meter reads 396.3 kWh. The following devices are switched on during the day:
60 W light bulb 3 hours
100 W light bulb 1.5 hours
1200 W hotplate 0.5 hours
Hot plate 240 W 2 hours
Iron 1000 W 2.5 hours
Radio 60 W 4.5 hours
How many kWh does the meter show in the evening?

Result: In the evening the counter shows 400.48 kWh.

13. When steaming up items of clothing, the regulator iron remains switched on (the control lamp does not go out).

A housewife spends 85 minutes steaming up skirts and men's trousers. Your iron has a connected load of 1000 W.
How high are the electricity costs if a kWh costs € 0.13?

Result: The energy costs are € 0.184

14. A trainee checks the meter reading on the washing day. It records 2435.7 kWh in the morning and 2459.9 kWh in the evening. One kWh costs 0.125 €.
Calculate electricity consumption and electricity costs.

Result: Energy: 24.2 kWh, costs: € 3.025.

15. Meter reading at 10:25 a.m. 1038.7 kWh, at 10:53 a.m. 1039.6 kWh.
Calculate the average power of the switched on device.

Result: The average power of the device is P = 1.927 kW

16. Meter reading on February 15, 12,997 kWh, on March 15, 13,420 kWh.
How high is the electricity bill if a kWh costs € 0.122 and a monthly fee of € 4.95 and 16% VAT?

Result: Energy: 423 kWh Cost: € 65.61.

17. The following lights up every day in an apartment:
2 light bulbs, each 25 watts, 4 hours
3 lightbulbs of 40 watts each for 3 hours
2 light bulbs of 75 watts each 3.5 hours
1 light bulb of 100 watts for 5 hours
What are the monthly energy costs for lighting if 1 kWh costs € 0.13 including VAT?

Result: The monthly energy costs are € 6.18.

18. Ms. Huber needs a hot water device and has to choose between a boiler and a storage tank.

She needs 80 liters of water a day with 85 0C.
You have the following offers: 80 liter boiler € 231.60
80 liter storage tank € 304.70
For heating 10 liters of water to 85 0C you need 1 kWh.
Daytime electricity € 0.122 per kWh, nighttime electricity € 0.068 per kWh
The storage system works with night power.
a) What are the monthly electricity costs for the boiler and the storage tank?
b) In what time are the higher acquisition costs of the storage brought in?

Result: a) Boiler energy costs: € 29.28, storage energy costs: € 16.32.
b) The higher acquisition costs of the storage unit are brought in in 5.64 months.

19. Ms. Meier has to choose between a boiler and a storage tank. She needs 120 liters of hot water every day (85 0C).
List prices: 120 liter boiler € 585.00
120 liter storage tank € 797.00
For heating 10 liters of water to 85 0C you need 1 kWh.
Daytime electricity € 0.122 per kWh, nighttime electricity € 0.068 per kWh
The storage tank would be heated with night electricity.
Which device should she choose?

Result: The higher acquisition costs of the storage tank are covered in 327 days by energy cost savings.

20. Washing one washing machine load of hot laundry (4.5 kg dry laundry) consumes 3.8 kWh of electricity. A household produces 18 kg of hot laundry per week.
a) The electricity costs per week if 1 kWh costs 0.125 €.
b) The cost of electricity per kg of dry laundry.

Result: The energy costs per week are € 1.90.
The energy costs per kg of dry laundry are € 0.106.

21. A fully automatic washing machine with a capacity of 4 kg has a connected load of 3200 W.

What are the weekly electricity costs for the washing machine, if per week
two drums of whites (95 0C),
a drum of colored laundry (60 0C),
a drum of delicates (60 0C) and
two drums of delicates (30 0C) be washed.
Energy requirement per washing machine filling:
Cottons 4.4 kWh, coloreds 3.2 kWh
Delicates 600 2.8 kWh, delicates 300: 2.0 kWh
One kWh costs 0.125 €.

Result: The weekly energy costs are € 2.35.

22. An electricity supply company (EVU) offers the following tariff for households (all prices including eco tax and VAT):

High tariff: Labor price: 0.1216 € / kWh, basic price: 59.30 € / year
Low tariff : Labor price at the high tariff period: 0.1432 € / kWh,
Labor price during the low tariff period (between 22:00 and 6:00): € 0.0682 / kWh
Base price: € 82.08 / year

a) How high are the monthly electricity costs if the electricity consumption is 135 kWh (high tariff)?
b) Annual electricity consumption in a household is 6600 kWh.
Calculate the annual electricity costs (high tariff)
c) Annual electricity consumption in a household is 6600 kWh.
Calculate the annual electricity costs, but assume that the low tariff has been used and that 45% of the energy is drawn between 10:00 pm and 6:00 am.

Result: a) The monthly energy costs are € 21.36.
b) The annual electricity costs are € 861.86.
c) The annual electricity costs are € 801.18.

23. A two-person household consumes 1950 kWh of electrical energy in one year.

What are the annual electricity costs?
Working price 0.1216 € / kWh, base price 59.30 € / year

Result: The annual energy costs are € 296.42.

24.Three people cook the same meat dish. It takes an hour to cook. Each person uses the electric plate with a diameter of 22 cm.
circuitpowerMrs. A.Mr. BMrs. C
Stage III1800 W60 minutes15 minutes15 minutes
Stage II1400 W45 minutes
Level I.300 W45 minutes
How high are the energy costs if 1 kWh cost € 0.13?
Result:Costs:0,234 €0,195 €0,0878 €


A lunch consists of:
Vegetable soup, roast pork, potato dumplings and raw salads.
It is cooked on the electric stove.
Soup10 minutes at level III
15 minutes at level I.
1800 W
600 W
roast meat35 minutes to 220 0C.
55 minutes to 200 0C.
1500 W
1200 W
Dumplings10 minutes at level III
10.0 minutes at level II
10 minutes at level I.
1500 W
1000 W
500 W

1 kWh costs € 0.13. Calculate the energy expenditure and the energy costs.

Result: The energy consumption is 2.925 kWh
The energy costs are € 0.2803.

26. Two housewives cook the same dish.

It consists of semolina dumpling soup and vegetable stew.

dishCooking timeHousewife AHousewife B
Soup1.5 hours1500 W15 minutes
1500 W
500 W
stew1 hour1800 W20 minutes
1800 W
600 W
a) How high are the electricity costs in each case? (1 kWh costs 0.125 €)
b) How much € can Ms. B save annually by switching back (if she cooks the same thing every day)?
Result:a) Energy costs:0,506 €0,25 €
b) Savings in 365 days:93,44 €

Here you will find the related theory of energy, work, performance in device science
and here is an overview of all articles on the topic of device science.

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