Five measurements of a 10.00cm rod yield: 10.4, 10.1, 10.2, 10.1, 10.4 cm. This demonstrates: @ Low accuracy, Low precision, @ High accuracy, Low precision, @ High precision, Low accuracy, @ Systematic error only

Five measurements of a $10.00 \, \text{cm}$ rod yield: $10.1, 10.1, 10.2, 10.1, 10.1 \, \text{cm}$.

Three molecules have speeds in $\text{m/s}$ as $2.00, 4.00$ and 5.00.

A $1000 \, \text{W}$ heater is $75\%$ efficient. The heater is used to increase the temperature of some water from $10^\circ\text{C}$ to $85^\circ\text{C}$ in $7 \, \text{hours}$. The specific heat capacity of water is $4200 \, \text{J/kgK}$.

What causes drift current in a p-n junction diode?

Drift current is the movement of charge carriers (electrons and holes) in a semiconductor due to the presence of an electric field. In a p-n junction, an electric field exists across the depletion region, which causes minority carriers to drift across the junction.

The correct answer is $\boxed{\text{a) Electric field}}$.

Which of the following is operated in forward bias?

• LED (Light Emitting Diode): An LED is specifically designed to emit light when current flows through it, which occurs when it is operated in forward bias.
• Solar cell: Solar cells typically operate in photovoltaic mode (zero bias, generating current from light) or can be reverse biased for certain applications.
• Photodiode: Photodiodes are usually operated in reverse bias (photoconductive mode) to detect light, as this increases the depletion region width and improves response time and sensitivity.
• Junction diode: This is a general term for a diode, which can be forward or reverse biased. However, among the specific devices listed, the LED's primary function relies on forward bias.

The correct answer is $\boxed{\text{a) LED}}$.

The main composition of biogas is?

Biogas is a mixture of gases produced by the anaerobic digestion of organic matter. Its primary components are methane ($\text{CH}_4$) and carbon dioxide ($\text{CO}_2$). Methane typically constitutes $50-75\%$ of biogas and is the main combustible component, making it the most significant part of its composition for energy purposes.

The correct answer is $\boxed{\text{b) Methane}}$.