Power in a Circuit
What is
POWER?
Power is the
rate of energy
transfer. It is
equal to the
product of
current and
voltage.
In equation form, it is given as
𝑃 = 𝐼𝑉
where;
P is power and its unit is the watt (W)
I is current and its unit is the ampere (A)
V is voltage and its unit is the volt (V)
Problem Solving 1
What is the power input to an electric
heater that draws 3 A from a 220 V
outlet?
Problem Solving 2
The heating element in clothes dryer
is rated at 5 Kw AND 220 V. How
much
current does it draw?
Electrical
Energy and
its Cost
Electric power is the rate of
energy transfer.
Electric companies like ZAMECO
charge us not the power but for
energy. The unit for energy used
by companies to calculate our
consumption is the kilowatt-hour
(kWh).
ENERGY in equation form, this
is given as
𝑊 = 𝑃𝛥𝑡
where;
W is Electrical energy and its unit is the Kilo-watt/hour
(kWh)
P is power and its unit is the watt (W)
t is time and its unit is the hour (hr)
Sample Problem
• How much does it cost to operate 20” desk fan
for 12 hours if the electrical energy costs
P4.57/kWh and wattage of desk fan of 79W?
Activity: Calculating
Operation Cost
Problem Solving 1
A ceiling fan has a power rating of 65 watts. If
the fan operates for 8 hours per day and the
cost of electricity is ₱5.00 per kWh, how much
will it cost to run the ceiling fan for 30 days?
Activity: Calculating
Operation Cost
Problem Solving 2
A laptop uses 45 watts of power while charging.
If it takes 3 hours to fully charge the battery
and the cost of electricity is ₱4.85 per kWh,
how much will it cost to charge the laptop 5
times?
Activity: Calculating
Operation Cost
Problem Solving 3
A refrigerator runs continuously at 150 watts.
If the electricity rate is ₱6.20 per kWh, how
much will it cost to operate the refrigerator
for 24 hours?
Activity: Calculating
Operation Cost
Problem Solving 4
An air conditioner consumes 1,200 watts when
running. If it operates for 6 hours a day and
the energy rate is ₱5.50 per kWh, how much will
it cost to operate the air conditioner for 15
days?
Activity: Calculating
Operation Cost
Problem Solving 5
A washing machine has a power rating of 500
watts. If it is used for 2 hours twice a week,
and the cost of electricity is ₱4.75 per kWh,
how much will it cost to operate the washing
machine in a month (4 weeks)?