2010 年

物理 · 共 43 題 · 點擊選項即時核對答案

只看錯題本頁已答 0 / 3

41.

Metal core with coil A connected to an a.c. supply through a switch and coil B connected to an a.c. voltmeter

The figure shows a metal core with two coils. When the switch is closed, the a.c. voltmeter shows a reading. Which of the following combinations will give the largest voltmeter reading ?

material of the metal core	no. of turns of coil $A$	no. of turns of coil $B$
copper	$500$	$1000$
copper	$1000$	$500$
iron	$500$	$1000$
iron	$1000$	$500$

42.

220 V mains with 5 A fuse, transformer and several identical 40 W bulbs in parallel

In the circuit above, the primary coil of a transformer is connected to the $220$ V mains supply with a $5$ A fuse. The efficiency of the transformer is $90\%$ . What is the maximum number of identical $40$ W light bulbs, operating at their rated values, that can be connected in parallel across the secondary coil without blowing the fuse ?

43.

In the figure, a $\beta$ particle enters a region with a magnetic field pointing into paper and an electric field of unknown direction. The $\beta$ particle has no deflection. What is the direction of the electric field ?

A beta particle moving to the right through a region with a magnetic field into the paper