Global Challenges | OCR GCSE Combined Science Physics, Higher tier (J250)
Global Challenges
- 145 questions
- 8 subtopics
- Paper 12 (Physics)
- Paper 12 (Physics)
Global Challenges is examined in Paper 12 (Physics).
It covers typical speeds and everyday accelerations, reaction time, stopping distance and the dangers of large decelerations, stopping distance, acceleration and collision force calculations, energy resources, and trends in their use, the national grid, and step-up and step-down transformers, why the national grid is efficient, and power in a transformer, mains electricity: a.c., d.c. and the domestic supply and live, neutral and earth wires, and electrical danger.
Sample questions from Global Challenges
Answer each one closed book first, then open the answer.
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Typical speeds and everyday accelerations
What does an acceleration of 2 m/s² mean in words?
Show the answer
The speed increases by 2 m/s during every second. -
Reaction time, stopping distance and the dangers of large decelerations
What is meant by the braking distance of a vehicle?
Show the answer
The distance travelled while the braking force acts, from the brakes being applied until the vehicle stops. -
Stopping distance, acceleration and collision force calculations
Estimate the resultant force on a 1000 kg car that is accelerating at 4 m/s².
Show the answer
4000 N. -
Energy resources, and trends in their use
Why is biofuel counted as renewable when burning it releases carbon dioxide?
Show the answer
The crops or waste it is made from can be regrown, and growing plants absorb carbon dioxide, so the resource is replaced as it is used. -
The national grid, and step-up and step-down transformers
What is a substation used for?
Show the answer
It houses transformers that lower the potential difference so the electricity can be distributed locally. -
Why the national grid is efficient, and power in a transformer
Besides using a high potential difference, how is energy loss in transmission cables kept low?
Show the answer
The cables are thick and made of a good conductor, which gives them a low resistance. -
Mains electricity: a.c., d.c. and the domestic supply
Why is the mains supply dangerous to touch?
Show the answer
About 230 V is large enough to drive a current through a person that can stop the heart or cause burns. -
Live, neutral and earth wires, and electrical danger
What is the potential difference between the neutral wire and earth?
Show the answer
About 0 V, because the neutral wire is held close to earth potential.
The 8 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Typical speeds and everyday accelerations | Typical speeds for walking, running, cycling, sound, wind, cars, trains and aeroplanes, what an acceleration in m/s² means, estimating the accelerations of cars, sprinters, cyclists and buses, and converting kilometres per hour, kilometres, tonnes and minutes for speed calculations. | 21 |
| Reaction time, stopping distance and the dangers of large decelerations | Typical reaction times, measuring them by ruler drop or computer and what lengthens them, thinking and braking distance and what increases each, why large decelerations injure and how crumple zones, seat belts and air bags help, overheated brakes and skids, and handling reaction-time data with averages, histograms, scatter diagrams and sampling. | 32 |
| Stopping distance, acceleration and collision force calculations | Adding thinking and braking distance to find a stopping distance, estimating thinking distance from speed and reaction time, estimating the accelerations and decelerations of cars, the resultant forces on an accelerating car and motorcycle and on a car in a crash, and why collision forces are so much larger than in ordinary driving. | 9 |
| Energy resources, and trends in their use | Renewable and non-renewable resources, how wind, hydroelectricity, tides, the Sun and biofuel are used, what energy resources are used for, trends in coal, gas, nuclear and renewables and the reasons behind them, and ethical questions about nuclear waste, dams and wind farms that science alone cannot settle. | 23 |
| The national grid, and step-up and step-down transformers | What the national grid is, the potential differences used for transmission and for homes, what substations do, and where step-up and step-down transformers sit and which coil has more turns. | 16 |
| Why the national grid is efficient, and power in a transformer | Why power = potential difference × current means a higher potential difference needs a smaller current, how the energy wasted in cables depends on the square of that current, why thick cables and one shared network help, and equal power in and out of an ideal transformer, with calculations. | 12 |
| Mains electricity: a.c., d.c. and the domestic supply | The UK mains supply as alternating current at 50 Hz and about 230 V, the length of one cycle, why the mains is dangerous, direct supplies from cells and adapters, how direct and alternating potential differences and their traces differ, and why a transformer needs an alternating supply. | 16 |
| Live, neutral and earth wires, and electrical danger | What the live, neutral and earth wires do, the potential differences between them and their colours, why a live wire is dangerous even with the switch open, how insulation, double insulation, the earth wire and a fuse protect the user, and why wet hands raise the danger. | 16 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR GCSE Combined Science Physics, Higher tier Active Recall Guide
Every topic, not just this one. 1,222 questions with their answers.