The main function of a step-up transformer is to

The total power $P_{\text{total}}$ is given by the product of voltage $V$ and current $I$.

The maximum number of bulbs $n$ is the total power divided by the power of a single bulb $P_{\text{bulb}}$.

The maximum number of bulbs is B. 16.

98. Which of the following statements about boiling and evaporation is correct?
Evaporation occurs at the surface of a liquid and can happen at any temperature below the boiling point. Boiling occurs throughout the liquid at a specific boiling temperature.
The correct option is D. evaporation takes place at a lower temperature than boiling does.

99. A body weighs 120N in air, and 80N in water. What is the density of the body in kgm⁻³?

The buoyant force $F_B$ is the apparent loss of weight when the body is immersed in water.

The buoyant force is equal to the weight of the displaced fluid ($F_B = \rho_{\text{water}} V_{\text{body}} g$). We can also relate the density of the body to the buoyant force.
The density of the body $\rho_{\text{body}}$ can be found using the formula:

Assuming the density of water $\rho_{\text{water}} = 1000 \, \text{kg/m}^3$.

The density of the body is D. 3000.

100. The principle of floatation states that
The principle of floatation (Archimedes' principle for floating objects) states that a floating body displaces a weight of fluid equal to its own weight.
The correct option is C. a floating body displaces its own weight of the fluid.

101. A mass of 400g was heated and immersed in an insulated copper calorimeter containing 200g of water at 16°C. If the temperature of the water and calorimeter of mass 400g goes to 60°C, find the initial temperature of the metal. (Specific heat capacities of aluminium, copper and water are 110J/KgK, 400J/KgK and 4200 J/KgK respectively.)

• Mass of metal $m_m = 400 \, \text{g} = 0.4 \, \text{kg}$
• Specific heat capacity of metal $c_m = 110 \, \text{J/kgK}$ (assuming the metal is aluminium, as it's the first specific heat given)
• Mass of water $m_w = 200 \, \text{g} = 0.2 \, \text{kg}$
• Specific heat capacity of water $c_w = 4200 \, \text{J/kgK}$
• Mass of calorimeter $m_c = 400 \, \text{g} = 0.4 \, \text{kg}$
• Specific heat capacity of calorimeter $c_c = 400 \, \text{J/kgK}$ (for copper)
• Initial temperature of water and calorimeter $T_{w,i} = T_{c,i} = 16^\circ \text{C}$
• Final temperature of mixture $T_f = 60^\circ \text{C}$
• Let the initial temperature of the metal be $T_{m,i}$.

Heat lost by metal = Heat gained by water + Heat gained by calorimeter.

The initial temperature of the metal is $\boxed{\text{}1060^\circ \text{C}}$.

102.a. What is a transformer?
A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It is used to increase or decrease alternating current (AC) voltages.