1. Do wires degenerate when electric current is passed through them? I mean, do they lose matter after continued use?
Wires made from
metals all conduct electric current by the motion of
electrons. Electrons move in (or out) of one end of a wire,
and an equal number move out (or in) the other end. This
balance is maintained by extremely powerful electric forces.
No net amount of matter is ever transferred when current
2. The US Antarctic programme advised its researchers to take loads of extra batteries when they visit, because batteries run down faster in cold weather. But I can't figure out why this is. Surely chemical reactions slow down in cold temperatures. Could it be the reason?
ELECTRIC current is produced by a battery when a connection is made between the positive and negative terminals via a piece of electrical equipment. The current is the result of a chemical reaction in the battery, and all such reactions proceed more slowly at low temperatures. It follows that if a battery is used at a low temperature, less current is produced at a given state of charge than at a higher temperature. So as batteries run down they more quickly reach the point at which they cannot deliver enough current. If the battery were exposed to a higher temperature again it would operate satisfactorily.
3. A lightning bolt recently struck the ground near my home, local telephones were damaged, fuses were blown and computers burned out, but other strange things happened. Some television sets switched on spontaneously and showed perfect pictures, yet those that were switched on normally after the strike had an odd color shift. Red became green, white became yellow and green became blue. If you switched them off for a minute, then on again, the problem was cured. Why did this happen? It might not be significant, but at the time of the strike, burglar alarms sounded spontaneously.
The peculiar results of the lightning strike can be explained by a mixture of electromagnetism and economics.
4. Walking through the countryside last weekend I noticed the overhead power lines were emitting a very loud hum. What causes this noise in high-voltage cables?
The hum is the result of the alternating electric field affecting water on the surface of the power line.
5. Considering the enormous amount of electrical energy contained in a lightning strike, why has no one tried to tap it for domestic use? Lightning energy is grounded by sending wired rockets into clouds, so could this energy be used?
It might sound like quite a nice idea, but there are several reasons why the answer is no. The first stems from the confusion of power with energy. Lightning strikes have a lot of power, but very little energy.
6. The oil refinery near my home sports a constantly burning flame. Other refineries around the world do the same. Why is this energy apparently wasted and why can't it be used as a power source?
In the early days of the oil industry, gas was a waste product and was just flared off. Nowadays, however, gas is a valuable commodity and is rarely thrown away. The flare your correspondent sees is only burning a very small proportion of the gas produced in the refinery, and is there as a safety measure.
7. Why does an electric bulb need to be vacuumed? Can we light up a bulb in the space without enclosing in the glass bulb?
An incandescent light bulb contains a thin wire filament that glows hot
when an electric current is run through it. In the presence of oxygen, the filament would
oxidise and burn up as a result of the high temperature. This occurs within a split second of switching on the bulb. So a glass bulb is used to cover the filament and extract the air away first, then keep oxygen
away from the filament.
8. I have noticed that household light bulbs sometimes develop a high-pitched hum before the filament fails. Can anyone suggest a mechanism for the humming?
When a filament breaks for the first time, the two severed ends may be so close together that electric current can still flow (arc) across the gap. So, the bulb will still function. However the path of the current now is very zigzag compared to the initial smoother path through the filament itself. So the disturbances produced by such randomly flowing and randomly striking electrons produces sound, which is being referred to as "Humming".Eventually the arcing erodes the severed ends of the filament and the bulb ceases to function.
9. How fast do electrons travel when moving as an electrical current through copper wire?
velocity of electrons through a conductor is measured as an
average speed called drift speed. This is because individual
electrons do not continue through the conductor in straight
line paths, but instead they move in a random zig-zag motion,
changing directions as they collide with atoms in the conductor.
Thus, the actual drift speed of these electrons through the
conductor is very small in the direction of current.
10. When someone gets electrocuted what kills him or her? Is it the current or the voltage?
The simple answer is that itís the current. The current passing through your body has lots of gruesome effects that were used for executions on the electric chair in America. Because itís not very easy for electricity to get through a human body, the current has to work hard. This heats up the body, literally cooking it.
11. Why donít we consider drift velocity of the positive ions in a conductor?
As the positive ions are heavily and tightly bound in the conductor, their movement due to force of applied electric field is nearly negligible. So, we don't consider drift velocity of the positive ions in a conductor.
12. It is dangerous to operate electrical appliances with wet hands. Why?
As our body behaves as a resistor having variable value of resistance. When we touch the electrical appliances by our wet hand then the resistance of our body decreases which results in the flow of large amount of current through our body than touched with our dry hands. Since wetness decreases the value of resistance and increases the rate of flow of current in our body according to the Ohm's law as given below:
where, I is the current flowing through resistor or resistance R and V iis the potential difference between the circuit.
Voltage remaining constant:
13. Why should an ammeter have low resistance?
As the purpose of ammeter is to measure the current flowing through the circuit, it is connected in series with the circuit. If the resistance of the ammeter is high then the net or effective resistance in the circuit is the sum of the resistances of the circuit and ammeter. This increases the value of the equivalent resistance of the circuit resulting in the decrease of the current. Hence, measured current will be less than actual current which cause the default result. Hence, an ammeter have low resistance.
14. Why should a voltmeter have high resistance?
The voltmeter is connected in parallel with the part of the circuit of which the potential difference is to be measured. If its resistance is low then the current of the circuit is distributed to both of the braches. Hence, measured p.d. of the circuit will be less than actual p.d. Hence, a voltmeter has high resistance.
15. Is Ohmís law applicable to all the conductors?
No, Ohm's law is applicable or valid for only ohmic conductors like metal, electrolytes etc. But it is not valid for non-ohmic conductors like semiconductors, ionized gases.
16. Can the resistance of metals become zero?
Generally, at higher temperature the resistance of metals can not be zero. But, the resistance of metal may become zero at very low temperature. The state of the metal in which the resistance becomes zero is called their super conducting state.
18. What are the values of current and p.d when a galvanometer reads zero?
At null point the galvanometer shows no deflection i.e. it reads zero. Hence, the value of current becomes zero as well as the value of potential difference becomes zero at the null point according to the Ohm's law:
where, V is the potential difference, I is the current flowing and R is the resistance of galvanometer.
19. Which has higher overall resistance, an ammeter or a galvanometer?
A galvanometer has higher overall resistance than an ammeter. As the ammeter is made from the galvanometer by adding one resistor having some resistance in parallel with the load. Hence, due to this arrangement the equivalent resistance of ammeter decreases due to which a galvanometer has higher overall resistance.
20. The electron drift speed is very small but an electric bulb lights up instantly when switched on, why?
The electric bulb lights up instantly when switched on because the electric impulse reaches the bulb instantly. The velocity if propagation of electric impulse is the same as that of the light.
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