Chapter 10 Multiple Choice Questions

1) The discoverer of the laws of electromagnetic induction was

Ampere.

Coulomb.

Faraday.

Volta.

2) Which of the following statements are true about a loop with N turns of area A, resistance R rotating with angular frequency ω in a uniform magnetic field B?
Please select all that apply.

The magnetic flux intersecting the loop is given by ϕ = N B A cos ω t

The electromotive force is given by ε = N B A sin ω t

The current is given by I = (N B Aω sin ω t) / R

3) Which of the following statements about electricity generators are true? Please select all that apply.

The frequency of mains electricity is chosen to avoid flickering of electric lights.

Eddy currents are suppressed by having a uniform core.

The power output of a three-phase generator is always non-zero.

4) Which of the following statements about high voltage AC transmission are true? Please select all that apply.

The fractional loss of power due to ohmic heating increases with line voltage.

Electric breakdown occurs at the surface of a conductor when the electric field exceeds the breakdown limit.

An overhead transmission cable consists of twisted strands of conducting wire.

The voltage is stepped-up from the power station to the overhead transmission line using transformers.

5) Which of the following statements about high voltage DC transmission are true? Please select all that apply.

DC is less suited than AC for underground power transmission.

AC is usually better than DC over long distances.

Rectification can be made by insulated gate bipolar transistors.

DC transmission is used for trans-national connections between different AC grids.

6) Which of the following statements about integrating renewables are true?
Please select all that apply.

At penetrations up to 40%, fluctuations in output can be met by spinning reserves.

The 'missing money problem', arises from too little renewable generation.

Good interconnection with neighbouring countries, together with its extensive CHP network, enables Denmark to manage its substantial wind capacity.

In China, investment in new transmission lines has reduced curtailment of wind and solar PV significantly.

Supply can always be altered to meet demand.

Wind and solar farms with storage are becoming as cheap as conventional stand-by generators.

7) On a grid with a lot of solar PV, the shape of the load met by conventional generators is called the _____ ______, but the peak conventional generating requirement can be reduced by ______ _______ some of the solar PV output.

8) The percentage of electricity from renewables can be raised on a grid by installing ______, increasing their _____ ______, by _______ with other grids, adding ______, and by altering the _____ to meet the ______.

9) Which of the following statements about a copper-zinc cell are true?
Please select all that apply.

The first copper-zinc cell was invented by Galvani.

The electrolyte used in a copper-zinc cell is dilute hydrochloric acid.

The energy required to remove an electron from copper is less than that for zinc

The standard potential is 1.1 V.

Zinc is the anode or negative electrode.

10) The relation between the Gibbs free energy ΔG^o, the number of electrons transferred n, the Faraday constant F, and the standard potential V ^o is…

ΔG^o = nFV^o^.

ΔG^o = −nFV ^o^.

V ^o = nFΔG^o.

V ^o = −nFΔG^o^.

11) Match the following statements about batteries.

11a.

Rechargeable

11b.

Non-rechargeable

11c.

Anode

11d.

Cathode

12) The movement of lithium ions into or out of a graphite electrode is called _______.

13) The cost per kWh for Li-ion batteries has fallen by a factor of about ___ over the period 2010–2019, and is expected to be about $100 by ____, making EVs then ______ with conventional ICE cars.

14) A Ragone plot for batteries is a plot of…

specific energy density versus specific power density.

charge density versus energy density.

output voltage versus stored charge.

stored charge versus cost.

15) The units of specific energy are…

W kg⁻¹.

J kg.

Wh kg⁻¹.

Wh.

Wh m⁻³.

16) Match the following specific energies in Wh kg⁻¹ to the fuel, battery, or bottle.

16a.

Petrol (gasoline)

16b.

Ethanol

16c.

Coal

16d.

Lead-acid battery

16e.

Li-ion battery

16f.

H₂ (700 bar) bottle

17) A flow battery…

has its energy stored in the electrolytes.

has a higher energy density than that of a Li-ion battery.

is not a good candidate for a grid storage battery.

separates its power and energy capacity.

has a specific energy density of about 20 Wh per kg.

18) Which of the following statements about a supercapacitor with an effective parallel plate area of 6000 m² g⁻¹ and a plate separation of 0.5 nm are true?
Please select all that apply.

It has a capacitance of order 100 F g^-1.

It can be discharged in about 1 second.

It has a specific power density comparable to an IC engine.

It has a specific energy density comparable to an IC engine.

19) Hydrogen produced by the electrolysis of water using power from renewables is called _______ ________ .

20) Which of the following statements about pumped storage are true?
Please select all that apply.

It is useful in countries with nuclear power stations.

The power output of a pumped storage reservoir is of the form P = ηρhQ where η is the efficiency.

It is useful for peak lopping.

It does not require a large amount of capital.

21) Which of the following statements about compressed air storage are true?
Please select all that apply.

It is not useful in countries with a lot of baseload generation.

Storage in large pressure vessels is uneconomic.

It is useful for peak lopping.

It is not suited for salt caverns because they are not gas-tight when under pressure.

22) Which of the following statements are true?
Please select all that apply.

Flywheels are not useful for peak-lopping.

Thermal stores cannot store energy for months.

It is more effective to make flywheels faster than heavier.

The storage efficiency is the main factor when considering energy storage.

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