Answer:
A permanent magnet creates a magnetic field at all points in the surrounding region.
An electric current in a conductor creates a magnetic field at all points in the surrounding region.
A moving electric charge creates a magnetic field at all points in the surrounding region.
Explanation:
Magnet field is a region around the magnet in which the magnetic force can be experienced. A magnet has two poles: North pole and South pole. A Magnetic field originates from north pole and ends at south pole.
Magnets are of two types: Permanent magnet and temporary magnet.
A moving charge produces magnetic field. A stationary charge can not produce a magnetic field.
The rate of flowing charge constitutes an electric current. If the cardboard is placed around the current carrying conductor and the iron fillings spread around the cardboard then the iron nails get stick to it. It means that a current carrying conductor creates a magnetic field around it.
Therefore, the true statements from the given statements are as follows;
A permanent magnet creates a magnetic field at all points in the surrounding region.
An electric current in a conductor creates a magnetic field at all points in the surrounding region.
A moving electric charge creates a magnetic field at all points in the surrounding region.
Answer:
ρ = 7500 kg/m³
Explanation:
Given that
mass ,m = 12 kg
Displace volume ,V= 1.6 L
We know that
1000 m ³ = 1 L
Therefore V= 0.0016 m ³
When metal piece is fully submerged
We know that
mass = Density x volume

Now by putting the values in the above equation

ρ = 7500 kg/m³
Therefore the density of the metal piece will be 7500 kg/m³.
We can solve the problem by using the first law of thermodynamics:

where
is the change in internal energy of the system
is the heat absorbed by the system
is the work done by the system on the surrounding
In this problem, the work done by the system is

with a negative sign because the work is done by the surrounding on the system, while the heat absorbed is

with a negative sign as well because it is released by the system.
Therefore, by using the initial equation, we find

Answer:
D.None of these
Explanation:
The derivation of acceleration formula:
Let us call the 5kg mass
and the 4kg mass
. If the tension in the string is
then for the mass 
(1).
<em>(the negative sign on the right side indicates that acceleration is downwards)</em>
And for the mass 
(2).
<em> (the acceleration is upwards, hence the positive sign)</em>
Solving for
in the 2nd equation we get:
,
and putting this into the 1st equation we get:


Back to the question:
Using the formula for the acceleration we find


which is the acceleration that none of the given choices offer. Also, the acceleration of the two blocks is the same, because if it weren't, the difference in the instantaneous velocities of the objects would cause the string to break. Therefore, these two reasons make us decide that none of the choices are correct.