pxt-calliope/docs/reference/js/lessons/cascade/quiz.md

# strobe lightquiz

Learn how to create a blinking LED script with a for loop. #LED #screen #plot #docs

## Name

## Directions

Use this activity document to guide your work in the [light column cascade tutorial](/microbit/js/light-column-cascade/tutorial).

Answer the questions below while working on or after you finish the tutorial. Pay attention to the dialogs!

## 1. What is a for loop?

## 2. Consider the following code

```
for (let i = 0; i < 5; i++) {
    for (let j = 0; j < 5; j++) {
        led.plot(i, j)
    }
}
```

If the rectangle below represents a board that is 5 LEDs wide and 5 LEDs tall, place an X approximately all the locations where the LED is lighted. Explain why the LED is lighted there.

![](/static/mb/empty-microbit.png)

## 3. Consider the following code

```
for (let i1 = 0; i1 < 3; i1++) {
    for (let j1 = 0; j1 < 3; j1++) {
        led.plot(i1, j1)
    }
}
```

If the rectangle below represents a board that is 5 LEDs wide and 5 LEDs tall, place an X approximately all the locations where the LED is lighted. Explain why the LED is lighted there.

![](/static/mb/empty-microbit.png)

## 4. Consider the following code

```
for (let i2 = 0; i2 < 2; i2++) {
    for (let j2 = 0; j2 < 2; j2++) {
        led.plot(i2, j2)
    }
}
```

If the rectangle below represents a board that is 5 LEDs wide and 5 LEDs tall, place an X approximately where the LED is lighted. Explain why the LED is lighted there.

![](/static/mb/empty-microbit.png)

******************************

## ANSWER KEY

## Directions

Answer the questions below while working on or after you finish the tutorial.

## 1. What is a for loop?

Answers will vary. In general, for loop refers to the code that repeats for a fixed number of times. We specify the LED using x, y coordinates.

## 2. Consider the following code

```
for (let i3 = 0; i3 < 5; i3++) {
    for (let j3 = 0; j3 < 5; j3++) {
        led.plot(i3, j3)
    }
}
```

If the rectangle below represents a board that is 5 LEDs wide and 5 LEDs tall, place an X approximately where the LED is lighted. Explain why the LED is lighted there.

![](/static/mb/lessons/cascade-0.png)

This code turns on specific LED. Plot turns on the specified LED on the LED screen. We specify the LED using x, y coordinates. The code lights on the LEDs

x - the x coordinate or horizontal position (0,1,2,3,4)

y - the y coordinate or vertical position (0,1,2,3,4)

## 3. Consider the following code

```
for (let i4 = 0; i4 < 3; i4++) {
    for (let j4 = 0; j4 < 3; j4++) {
        led.plot(i4, j4)
    }
}
```

If the rectangle below represents a board that is 5 LEDs wide and 5 LEDs tall, place an X approximately where the LED is lighted. Explain why the LED is lighted there.

![](/static/mb/lessons/cascade-1.png)

This code turns on specific LED. Plot turns on the specified LED on the LED screen. We specify the LED using x, y coordinates.

x - the x coordinate or horizontal position (0,1,2)

y - the y coordinate or vertical position (0,1,2)

## 4. Consider the following code

```
for (let i5 = 0; i5 < 2; i5++) {
    for (let j5 = 0; j5 < 2; j5++) {
        led.plot(i5, j5)
    }
}
```

If the rectangle below represents a board that is 5 LEDs wide and 5 LEDs tall, place an X approximately where the LED is lighted. Explain why the LED is lighted there.

![](/static/mb/lessons/cascade-2.png)

This code turns on specific LED. Plot turns on the specified LED on the LED screen. We specify the LED using x, y coordinates.

x - the x coordinate or horizontal position (0,1)

y - the y coordinate or vertical position (0,1)