Page 70 - Maxwell House

50 Chapter 2

Alternatively, the electricity generation is expected as soon as the rotary force and torque

is created, for example, by cranking the
handle, as shown in Figure 2.1.4, or using as
well energy of falling water, steam, or wind to
rotate mechanically the conductive loop
between the poles of a permanent magnet. In
1833 the German scientist Heinrich Lenz
published an article about the law of
reciprocity for the magneto-electric and
electromagnetic phenomena, i.e. the
reversibility of electric motor and generator
and possibility to convert mechanical energy
back to electrical. The EMF ℰ() measured by
voltmeter in Figure 2.1.4 can be estimated
2
Figure 2.1.4 Hand crank AC generator from Faraday’s law (1.42). Since ∘ =
cos and in the process of rotation, the
angle between vector B and varies

(cos )
ℰ() = − ∬ ∘ = − (2.5)

Assuming that the angular speed of rotation is equal to ω [rad/s] and thus = , we obtain
from (2.5)
ℰ() = sin (2.6)

Therefore, the device in Figure 2.1.4 is the
converter or AC generator transforming the
mechanical energy to EM energy. Eventually,
the output voltage increases approximately N
times when N loops are connected in series as
it is shown schematically in Figure 2.1.5 .
3
According to (2.6), there are several additional
ways to generate more power using, for
example, a stronger magnet ( ↑), increasing
rotation frequency ( ↑) and loop area ( ↑),
Figure 2.1.5 Multi-coil AC generator or all together. Modern high power generator
is quite impressive machinery of multi-story
building sizes. Typically, in such generator the permanent magnet is rotated inside the cage
formed by the wire loops at rest.

The above discussion could create a false impression that electric generators are capable to
“create” electrical energy. It is not true because they used such forms of energy as mechanical,
chemical, light, heat, and others to separate forcefully positive and negative electric charges
naturally existing in any solid (copper wires), liquid or gas medium and ultimately retain such
separation. And only after all, the forces exerted by electric and magnetic fields move these
charges through an external electric circuit.

2 Public Domain Image, source: https://www.pinterest.com/pin/205054589259310874/
3 Public Domain Image, source: https://www.pinterest.com/franzkronenberg/ok/