The resistance of the lamp is apparently 50V/2A = 25 ohms.
When the circuit is fed with more than 50V, we want to add
another resistor in series with the 25-ohm lamp so that the
current through the combination will be 2A.
In order for 200V to cause 2A of current, the total resistance
must be 200V/2A = 100 ohms.
The lamp provides 25 ohms, so we want to add another 75 ohms
in series with the lamp. Then the total resistance of the circuit is
(75 + 25) = 100 ohms, and the current is 200V/100 ohms = 2 Amps.
The power delivered by the 200V mains is (200V) x (2A) = 400 watts.
The lamp dissipates ( I² · R ) = (2² · 25 ohms) = 100 watts.
The extra resistor dissipates ( I² · R) = (2² · 75 ohms) = 300 watts.
Together, they add up to the 400 watts delivered by the mains.
CAUTION:
300 watts is an awful lot of power for a resistor to dissipate !
Those little striped jobbies can't do it.
It has to be a special 'power resistor'.
300 watts is even an unusually big power resistor.
If this story actually happened, it would be cheaper, easier,
and safer to get three more of the same kind of lamp, and
connect THOSE in series for 100 ohms. Then at least the
power would all be going to provide some light, and not just
wasted to heat the room with a big moose resistor that's too
hot to touch.
Efficiency = (Wanted) energy out ÷ energy in × 100
Energy in = 400J
Wanted Energy out = 240J
Energy cannot be used up, only transferred, so the remaining energy is most likely to be transferred into unwanted energy (loss of energy) such as heat energy.
Efficiency = 240 ÷ 400 × 100
Efficiency = 0.6 × 100
Efficiency = 60%
Answer:
m = 3.91 kg
Explanation:
Given that,
Mass of the object, m = 3.74 kg
Stretching in the spring, x = 0.0161 m
The frequency of vibration, f = 3.84 Hz
When the object is suspended, the gravitational force is balanced by the spring force as :
k = 2276.52 N/m
The frequency of vibration is given by :
m = 3.91 kg
So, the mass of the object is 3.91 kg. Hence, this is the required solution.
<u>Halfway</u><u> between the like poles of two magnets, because the field lines bend away and do not enter this area.</u>
How does a magnetic field diagram show where the field is strongest?
- The magnetic field lines do not ever cross.
- The lines include arrowheads to indicate the direction of the force exerted by a magnetic north pole.
- The closer the lines are to the poles, the stronger the magnetic field (thus the magnetic field from a bar magnet is highest closest to the poles).
Where is magnetic field the strongest and weakest on a magnet?
- The bar magnet's magnetic field is strongest at its core and weakest between its two poles.
- The magnetic field lines are densest immediately outside the bar magnet and least dense in the core.
Which two locations on the magnet would have the greatest attractive forces?
- Inside the magnet itself, the field lines run from the south pole to the north pole.
- The magnetic field is strongest in areas of greatest density of magnetic field lines, or areas of the greatest magnetic flux density.
Learn more about magnetic field
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