David Sang and Graham Jones Solutions for Chapter: Electric Current, Potential Difference and Resistance, Exercise 12: EXAM-STYLE QUESTIONS

Some electricity-generating companies use a unit called the kilowatt-hour $\left(\mathrm{kWh}\right)$ to calculate energy bills. $1\mathrm{kWh}$ is the energy a kilowatt appliance transfers in $1$ hour.

(a) Show that $1\mathrm{kWh}$ is equal to $3.6\mathrm{MJ}$.

Some electricity-generating companies use a unit called the kilowatt-hour $\left(\mathrm{kWh}\right)$ to calculate energy bills. $1\mathrm{kWh}$ is the energy a kilowatt appliance transfers in $1$ hour.

(b) An electric shower heater is rated at $230 \mathrm{V},9.5 \mathrm{kW}$.

(i) Calculate the current it will take from the mains supply.

Some electricity-generating companies use a unit called the kilowatt-hour $\left(\mathrm{kWh}\right)$ to calculate energy bills. $1\mathrm{kWh}$ is the energy a kilowatt appliance transfers in $1$ hour.

(b) An electric shower heater is rated at $230 \mathrm{V},9.5 \mathrm{kW}$.

(ii) Suggest why the shower requires a separate circuit from other appliances.

Some electricity-generating companies use a unit called the kilowatt-hour $\left(\mathrm{kWh}\right)$ to calculate energy bills. $1\mathrm{kWh}$ is the energy a kilowatt appliance transfers in $1$ hour.

(b) An electric shower heater is rated at $230 \mathrm{V},9.5 \mathrm{kW}$.

(iii) Suggest a suitable current rating for the fuse in this circuit.

Some electricity-generating companies use a unit called the kilowatt-hour $\left(\mathrm{kWh}\right)$ to calculate energy bills. $1\mathrm{kWh}$ is the energy a kilowatt appliance transfers in $1$ hour.

(c) Calculate the energy transferred when a boy uses the shower for $5$ minutes.

A student is measuring the resistance per unit length of a resistance wire. He takes the following measurements.

(a) Calculate the percentage uncertainty in the measurement of the current.

A student is measuring the resistance per unit length of a resistance wire. He takes the following measurements.

(b) Calculate the value of the resistance per unit length of the wire.

A student is measuring the resistance per unit length of a resistance wire. He takes the following measurements.

(c) Calculate the absolute uncertainty of the resistance per unit length of the wire.