energy transfers

Question 1

power

Answer 1

power = potential difference × current
P = V I

Question 2

power and current

Answer 2

power = current2 × resistance
P = I2 R
power, P, in watts, W
potential difference, V, in volts, V
current, I, in amperes, A (amp is acceptable for
ampere)
resistance, R, in ohms, Ω

Question 3

Students should be able to explain how the power
transfer in any circuit device is related to the potential
difference across it and the current through it, and to
the energy changes over time.

Answer 3

Power Transfer:

Power (
𝑃
P) is the rate at which energy is transferred or converted in a circuit device.
The power transferred in a device depends on the potential difference (V) across the device and the current (I) flowing through it.
Formula for Power:

The power
𝑃
P in an electrical circuit is given by the formula:
𝑃
=
𝑉
×
𝐼
P=V×I
Where:
𝑃
P is the power (measured in watts, W),
𝑉
V is the potential difference (measured in volts, V),
𝐼
I is the current (measured in amperes, A).
Energy Changes Over Time:

The energy
𝐸
E transferred over time (
𝑡
t) is related to the power and the time for which the current flows. The formula is:
𝐸
=
𝑃
×
𝑡
E=P×t
Where:
𝐸
E is the energy (measured in joules, J),
𝑃
P is the power (measured in watts, W),
𝑡
t is the time (measured in seconds, s).
Relationship Between Power, Voltage, and Current:

The power in a circuit device increases if either the current or the potential difference increases.
For example, if you increase the voltage across a device, the power increases (assuming the current remains constant), and if you increase the current through the device, the power also increases (assuming the potential difference remains constant).

Question 4

Describe how different domestic appliances transfer
energy from batteries or ac mains to the kinetic
energy of electric motors or the energy of heating
devices

Answer 4

Electrical energy (from batteries or AC mains) is transferred to appliances.
In electric motors (e.g., in fans, vacuum cleaners), electrical energy is converted into kinetic energy (movement).
In heating devices (e.g., kettles, toasters, heaters), electrical energy is converted into thermal energy (heat).
Electric motors use the flow of electrical current to generate movement (kinetic energy).
Heating devices use electrical resistance to generate heat energy, which is then transferred to the object being heated.