Electrical System (Should heating element have high resistance or low resistance?) | The Brainy Couple

This is a question that confuses many, especially those who are just beginning to learn about electricity.

Should heating element have high resistance or low resistance? Before that, follow me, here is the basic understanding.

Should heating element have high resistance or low resistance? By right, V=IR. If voltage EMF is constant, when R decrease, Current should increase. Q) Why can't we touch the switch with wet hands? Water reduces the electrical resistance of our hands So if electricity is leaking from switch, it will flow down our hands with high current, Out through our feet then to ground, Causing electricity shock Q) Why should workers wear rubber boots when working with electricity? If electricity is leaking, without the rubber boots, electricity will flow through our body (70% water) to the ground, however with rubber boots which is a electrical insulator, there is no closed circuit for electricity to flow through, hence we won't get electric shock. Q) What is a short circuit? It is a low resistance connection between the two conductors supplying electrical power to any circuit, where all current prefer to flow through the resistor with much lower resistance. This results in excessive current flow in the power source through the low resistance connection.

Should heating element have high resistance or low resistance? Now, for heating element to release large amount of heat energy, shouldn't current be high, which means resistance should be low? Not really. Because the voltage supplied to heating element is not constant, while the current to the heating element is kept constant, unlike the examples above. Q) Why does heating element have much higher resistance (than the connecting wires)? Energy lost per second = Power = V2/R or I2R To produce more thermal energy per second, it should have higher resistance. Because Total Voltage x (High) Resistance of heating element/ Total Resistance = High Voltage allocated to heating element, hence heating element can produce more thermal energy. (Of course if the resistance is too high, it can't even conduct electricity) Q) Why does metal wires have low resistance in general? Metal wires should have much lower resistance than the load (heating element) So that less energy is drawn from the source to be lost as heat (which may melt the wire insulator)

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Q) What are the possible fault in electrical appliances?

The fault could be due to:

  • Conductors (e.g. wires, terminals, components) at hot or near full mains potential breaking, bending or detaching and touching the casing of the appliance
  • Breakdown of insulation. For instance, insulation on cores of the power flex could become damaged inside an appliance or insulating spacers could become dislodged. Also, metal parts such as screws or nuts which have come undone could bridge the gap between hot and the metal casing
  • Making contact with a power cable when drilling through a wall

From <https://dengarden.com/home-improvement/Waht-is-The-Ground-Wire-For>

Q) What is a hot / live wire?

Current flows out from source through this wire to an appliance.

Q) What is a neutral wire?

The neutral wire is at a voltage close to or equal to ground. Current which flows to an appliance via the hot wire returns via the neutral core in a cable


Do take note of the difference between earth wire, neutral wire, grounding too 🙂

Nervous System Notes | Coordination and Response Notes 5/5

Nervous System Checklist O Levels

Candidates should be able to: (a) state the relationship between receptors, the central nervous system and the effectors (b) describe the structure of the eye as seen in front view and in horizontal section (c) state the principal functions of component parts of the eye in producing a focused image of near and distant objects on the retina (d) describe the pupil reflex in response to bright and dim light (e) state that the nervous system – brain, spinal cord and nerves, serves to co-ordinate and regulate bodily functions (f) outline the functions of sensory neurones, relay neurones and motor neurones (g) discuss the function of the brain and spinal cord in producing a co-ordinated response as a result of a specific stimulus in a reflex action (h) define a hormone as a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver (i) explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the pancreas

Candidates should be able to:
(a) state the relationship between receptors, the central nervous system and the effectors
(b) describe the structure of the eye as seen in front view and in horizontal section
(c) state the principal functions of component parts of the eye in producing a focused image of near
and distant objects on the retina
(d) describe the pupil reflex in response to bright and dim light
(e) state that the nervous system – brain, spinal cord and nerves, serves to co-ordinate and regulate
bodily functions
(f) outline the functions of sensory neurones, relay neurones and motor neurones
(g) discuss the function of the brain and spinal cord in producing a co-ordinated response as a result
of a specific stimulus in a reflex action
(h) define a hormone as a chemical substance, produced by a gland, carried by the blood, which
alters the activity of one or more specific target organs and is then destroyed by the liver
(i) explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the
pancreas