Which is true of a step-down transformer but not a step-up transformer? The core is made of copper and the coils are made of iro
2 answers:
The primary winding has more coils than the secondary winding
Explanation:
A transformer is a device consisting of two coils (called primary and secondary coil) wrapped around a soft iron core. As the primary coil is connected to alternate voltage, a variable magnetic field inside the iron core is produced; the lines of this field cut also the secondary coil, and due to the phenomenon of electromagnetic induction, an e.m.f is produced in the secondary coil (so, an alternate voltage).
The voltages in the two coils are related by the transformer equation:
(1)
where
is the voltage in the primary coil
is the voltage in the secondary coil
is the number of turns in the primary coil
is the number of turns in the secondary coil
In a step-down transformer, the voltage in the secondary coil is lower than the voltage in the primary coil (they are used to decrease the voltage in input), therefore:
which means, according to eq.(1),
So
Therefore the correct answer is
The primary winding has more coils than the secondary winding.
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Answer:
C) 7.35*10⁶ N/C radially outward
Explanation:
- If we apply the Gauss'law, to a spherical gaussian surface with radius r=7 cm, due to the symmetry, the electric field must be normal to the surface, and equal at all points along it.
- So, we can write the following equation:
- As the electric field must be zero inside the conducting spherical shell, this means that the charge enclosed by a spherical gaussian surface of a radius between 4 and 5 cm, must be zero too.
- So, the +8 μC charge of the solid conducting sphere of radius 2cm, must be compensated by an equal and opposite charge on the inner surface of the conducting shell of total charge -4 μC.
- So, on the outer surface of the shell there must be a charge that be the difference between them:
- Replacing in (1) A = 4*π*ε₀, and Qenc = +4 μC, we can find the value of E, as follows:
- As the charge that produces this electric field is positive, and the electric field has the same direction as the one taken by a positive test charge under the influence of this field, the direction of the field is radially outward, away from the positive charge.