2 . It would be much more convenient if electric cars could be recharged wirelessly. Some electric toothbrushes and other small devices, such as mobile phones, can already be topped up in this way using a process called electromagnetic induction (电磁感应). This employs some kind of electrical current flowing through a coil (线圈) to create a varying magnetic field, which then generates another current in a second coil placed alongside it, which is used to recharge a battery.
As users of electric toothbrushes and phones will know, device and charger must be both close to each other and precisely adjusted for this process to work. That is tricky to achieve with an electric car, which sits above the ground and requires higher levels of energy transfer.
These problems are being overcome with advances like that made by WiTricity, a firm based near Boston. This company was founded in 2007 to commercialize the work of Marin Soljaèi and his colleagues at the Massachusetts Institute of Technology. Dr Soljaëi knew, in theory, that by having the transmitting and receiving coils resonate (共振) at the same frequency it should be possible to transfer greater amounts of energy over longer distances. In practice, he sought to commercialize the system to large companies, such as BMW.
An advantage of wireless recharging is what WiTricity’s boss calls “power snacking”. This is topping up the battery when a car is stationary for a short time. The company provides systems to recharge taxis in this way while they wait in line, and to do the same for electric buses at bus stops. It is also possible to charge vehicles while they are on the move. That might make sense in places where vehicles often queue up, such as at airports.
1. How can electric devices be charged wirelessly?
| A．By devices close to chargers. |
| B．By high levels of energy transfer. |
| C．By an electrical current flowing through a coil. |
| D．By a process of electrical currents transformation. |
2. What makes it possible for electric cars to get lots of energy wirelessly?
| A．Commercializing the system to BMW. |
| B．Charging vehicles while they are on the move. |
| C．The transformation of energy over longer distances. |
| D．The good cooperation between the transmitting and receiving coils. |
3. What does the underlined word “stationary” in paragraph 4 probably mean?
| A．Moving. | B．Motionless. | C．Firm. | D．Unchanging. |
4. Which might be the most suitable title for the text?
| A．Various forms of wireless-charging systems. |
| B．Advantages and disadvantages of wireless-charging. |
| C．How to charge a car with a wireless-charging system. |
| D．Wireless vehicle-charging is starting to look promising. |
