4.A Electricity and Magnetism Pre Assessment
... build up of charge that can be released. A closed circuit is
needed to light a bulb in a circuit. Switches open and close
circuits. Metals conduct electricity. Electricity can be
changed into heat, light, sound, or motion.
Lesson 12. Topic “Early history of electricity” Grammar material: The
... shocks which could be obtained by a person coming into contact with the electric fish.
Nobody knew that the above phenomena were due to electricity. People could neither
understand their observations nor find any practical applications for them.
As a matter of fact, all of man's knowledge in the fie ...
Electricity on Shabbat
Many Jews who strictly observe Shabbat (the Sabbath), especially within Orthodox Judaism, refrain from what is considered turning electricity on or off during Shabbat. They may also refrain from making adjustments to the intensity of electrical appliances. Various rabbinical authorities have pronounced on what is permitted and what is not, but there are many disagreements in detailed interpretation, both between different individual authorities and between branches of Judaism.Orthodox authorities of Jewish law have disagreed about the basis of this prohibition since the early 20th century. Many Orthodox leaders have held that turning on an incandescent light bulb violates the Biblical prohibition against igniting a fire (Hebrew: הבערה, hav’arah). However, the reasons for prohibiting the operation of an electrical appliance that does not produce light or heat, such as an electric fan, are not agreed upon. At least six substantive reasons have been suggested, and a minority believe that turning on an electrical fan is prohibited only because of common Jewish practice and tradition (minhag) but not for any substantive technical reason. Conservative Jewish authorities have argued that such reasons do not justify describing the use of electricity as prohibited.Although directly operating electrical appliances is prohibited in Orthodoxy, several indirect methods are permitted according to some or all authorities. For example, Jews may look at the time on a clock, or set a timer before Shabbat to operate a light or appliance on Shabbat, and in some cases they may adjust the timer on Shabbat. Actions which activate an electrical appliance but are not specifically intended to do so may be permitted if the activation is not certain to occur or if the person does not benefit from the automatic operation of the appliance. For example, most authorities permit Jews to open a refrigerator door even though it may cause the motor to turn on immediately or later (not certain to occur); however, they prohibit opening the door if a light inside will automatically turn on (certain and of benefit). They also permit walking past a house with a motion sensor which switches on a light if the street is already well-lit (not of benefit), but not if it is dark.Some uses of electricity are especially controversial in the state of Israel because of its majority Jewish population. The use of automated machines to milk cows on Shabbat, an activity that is prohibited if done by hand, is disputed because the farmer may derive economic benefit from the milk, although cows suffer if not milked regularly. The use of electricity from power plants operated by Jews in violation of Shabbat is also controversial because it is normally forbidden to benefit from the action of another Jew in violation of Shabbat. However, because of communal need and other halakhic factors, most religious authorities in Israel permit these uses of electricity.Laws pertaining to the use of electricity on the Sabbath are followed mostly by Orthodox Jews. Non-Orthodox Jews who observe the Sabbath, such as Conservative and Reform Jews, take a less restrictive view or choose not to limit the use of electricity at all. Some Conservative Jews, for example, consider electricity to be like running water—it can be turned on and off at the tap without igniting or extinguishing a fire, and therefore may be used on the Sabbath. Conservative Judaism allows the use of electricity on Shabbat as long as it does not promote any Shabbat-prohibited activity.