1. Figure A (a curve) shows the activity of A/Br against time while Figure B (a curve) shows the activity of B/Bq against time. The y-intercept of figure A is 600, and note that the activity of A is 300 and the time is 10 min. And the activity of B/ Bq is 600, and note that the activity of B is 150 and the time is 10 min. The two diagrams show the variation of the activities of two radioactive sources A and B with time. What is the ratio of the half-time of A to that of B?
2. State the statements are true or not.
Statement 1: When sound wave travels from air to water, its frequency increases.
Statement 2: When speed wave travels from air to water, its speed increases.
Statement 1: Liquid has fixed volume.
Statement 2: Molecules in liquid do not move at all.
Satement 1: α-particles has lower ionizing power than ϐ particle.
Satement 2: The average speed of α-particles is smaller than that of ϐ particle.
3. In the circuit, the rating of each light bulbs is "50W, 20V". The current in the primary coil is 1.2 A. If all the bulbs work at their rated values, find the turns ratio and efficiency of the transfer. Note that the main is 220 V.
4. Electical power can be transmitted from power station to a distinct factory through device X, long transmitting cable and device Y. Device X and Y are?
5. diagram A and B have constant voltage supply. The resistance is placed near the voltage supply. Bulb P and Q are placed in parallel. Bulb R and S are also placed in parallel and the resistance is placed near the bulb S. Bulb P, Q , R and S are identical. What happen to the brightness of P and R if the switch of both circuits are closed?
更新1:
For Q.2, please explain them. Not speed wave, it should be sound wave.
更新2:
Not satisfy.
