物理家居用電 DSE、CE 選擇題

1.

As shown in the figure, a $2$ W light bulb is immersed into $50$ g of water. The bulb is operating at its rated value. After $10$ minutes, the temperature of the water increases by $4.5^\circ\mathrm{C}$ . Estimate the amount of light emitted during the $10$ minutes. Given : specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$

Light bulb immersed in water in a transparent plastic cup with foam cover and thermometer

2.

The photo below shows the back of a microwave oven.

Photograph of the back of a microwave oven with label: power supply 220 V - 50 Hz, power consumption 1150 W, microwave output 750 W, microwave frequency 2450 MHz

Which of the following statements is/are correct ?

(1)The current flowing through the microwave oven is about

3.4

A.

(2)Around

65\%

of electrical energy is converted into energy carried by microwave.

(3)The wavelength of the microwave emitted is about

0.12

m.

3.

Circuit with 9 V battery, two resistors R in parallel, in series with a bulb

In the circuit above, the rating of the bulb is " $6$ V, $12$ W". Find the resistance of $R$ so that the bulb will work at its rated value.

4.

Electric kettle with live, neutral (with switch S and fuse) and earth wires, point P and metal case

In the figure above, the kettle is wired incorrectly. Which of the following statements is correct when point $P$ is accidentally connected to the metal case ?

5.

Two identical bulbs, $X$ and $Y$ , are connected in parallel to the mains. The current passing through $X$ is $0.4$ A. What is the energy consumed by the two bulbs in $5$ hours ?

Two bulbs X and Y connected in parallel to a 220 V supply

6.

The power ratings and resistances of two light bulbs are " $24$ W, $6\ \Omega$ " and " $9$ W, $4\ \Omega$ " respectively. If these two light bulbs are connected in parallel to a power supply, what is the maximum current drawn from the power supply so that both light bulbs are working within the rated power ?

7.

Electric kettle with wires X, Y (through a switch and fuse) and Z

Which of the following is the correct connection of $X$ , $Y$ and $Z$ to the mains ?

$X$	$Y$	$Z$
live	earth	neutral
live	neutral	earth
neutral	earth	live
neutral	live	earth

8.

A mains heater has two identical heating elements of same resistance $R$ .

Heater circuit with two resistors R and switches S1, S2 and S3 connected to the mains

When $S_1$ and $S_2$ are closed and $S_3$ is open, the power of the heater is $P$ . What is the power of the heater when $S_1$ and $S_2$ are open and $S_3$ is closed ?

9.

A lighting system consists of $3$ bulbs, each rated ' $220$ V $30$ W'. These three bulbs should be connected in parallel to the $220$ V mains supply. However, the bulbs are wrongly connected in series to the mains supply. What is the power dissipation of the wrongly connected system ?

10.

A household circuit breaker is marked ' $220$ V, $15$ A'. Now an electric iron rated ' $220$ V, $1100$ W' and a cooker rated ' $220$ V, $550$ W' are connected to a mains socket. How many light bulbs rated ' $220$ V, $100$ W' at most can still be connected in parallel to the mains without triggering the circuit breaker ?