Electrical Engineering All Engineering Career

The international ohm is defined in terms of the resistance of a column of mercury.

Voltage dependent resistors are usually made from silicon carbide.

In a series circuit, the quantity that remains the same in all parts is current.

To find the length of the nichrome wire required for the heater coil, we can use the formula:

\[ P = \dfrac{V^2}{R} \]

Where:
- \( P \) is the power (in watts)
- \( V \) is the voltage (in volts)
- \( R \) is the resistance (in ohms)

Given:
- \( P = 1000 \) W (1 kW)
- \( V = 200 \) V
- \( R = 2 \) ohms/m

First, let's calculate the total resistance \( R_{\text{total}} \) of the wire needed for the heater coil:

\[ R_{\text{total}} = \dfrac{V^2}{P} \]

\[ R_{\text{total}} = \dfrac{200^2}{1000} \]

\[ R_{\text{total}} = 40 \, \Omega \]

Now, we can use the resistance per meter of wire to find the length \( L \) required:

\[ R_{\text{total}} = R \times L \]

\[ 40 = 2 \times L \]

\[ L = \dfrac{40}{2} \]

\[ L = 20 \, \text{m} \]

So, the length of wire required for the heater coil is 20 meters.

In a lamp load, when more than one lamp are switched on, the total resistance of the load decreases.

This is because when lamps are connected in parallel, the total resistance of the circuit decreases, leading to an increase in current flow and therefore an increase in the overall brightness of the lamps.

When electric current passes through a bucket full of water and bubbling is observed, it suggests that the type of supply is DC (direct current).

This bubbling is typically due to the electrolysis of water, where the water molecule (H₂O) is split into hydrogen gas (H₂) and oxygen gas (O₂) in the presence of an electric current. This process occurs more prominently with DC supply compared to AC supply.

The weight of an aluminum conductor, compared to a copper conductor of identical cross-section, for the same electrical resistance is approximately 50%. Aluminum has higher resistivity than copper, so an aluminum conductor needs to have a larger cross-sectional area to achieve the same resistance as a copper conductor. As a result, the aluminum conductor will be lighter for the same resistance.

The condition for the validity of Ohm's law is that the resistance must be uniform. This means that the resistance of the conductor should remain constant, and the material should obey Ohm's law over the range of voltages and currents applied.

The supply wiring does not glow because the resistance of the heater coil is more than the supply wires. The heater coil is designed to have a higher resistance, which causes it to heat up and glow when current flows through it. In contrast, the supply wires have lower resistance and are typically made of materials with higher melting points, so they do not heat up enough to glow.

The materials having electrical conductivity much less than most metals but much greater than that of typical insulators are called semiconductors.