Momentum = mass x velocity
12 = 4 x v | ÷ both sides by 4
12 ÷ 4 =v
v= 3 m/s
By definition we have to:
The electric current is the flow of electric charge due to the movement (usually of electrons) that a material travels.
Some properties are:
1) Electric conduction: The conductive materials have a large amount of free electrons, therefore, the passage of electricity is possible.
2) The current inside a circuit is directly proportional to the voltage and inversely proportional to the resistance of the circuit. This is what is known as ohm's law:

3) The current can be continuous or alternate.
Alternating current is the electric current in which the magnitude and direction vary cyclically.
The direct current is the flow of electric charges that does not change direction with time.
Answer:
B) waves speed up
C) waves bend away from the normal
Explanation:
The index of refraction of a material is the ratio between the speed of light in a vacuum and the speed of light in that medium:

where
c is the speed of light in a vacuum
v is the speed of light in the medium
We can re-arrange this equation as:

So from this we already see that if the index of refraction is lower, the speed of light in the medium will be higher, so one correct option is
B) waves speed up
Moreover, when light enters a medium bends according to Snell's Law:

where
are the index of refraction of the 1st and 2nd medium
are the angles made by the incident ray and refracted ray with the normal to the interface
We can rewrite the equation as

So we see that if the index of refraction of the second medium is lower (
), then the ratio
is larger than 1, so the angle of refraction is larger than the angle of incidence:

This means that the wave will bend away from the normal. So the other correct option is
C) waves bend away from the normal
Current at all points of a series circuit must be the same, because there's no place in the circuit where electrons are being manufactured, and no place where they're leaking out and falling on the floor. The nimber of electrons that leaves the loop is the same number that entered it.
I'm not sure what is nmeant by "p.d. remains different" .