Past Simple - Present Perfect

Exact Language for Lab Safety

Here's the scenario.

You are working in a lab and have to heat a solution with a burner for exactly 30 minutes. After a while you ask your lab partner to check on it. They tell you one of the following sentences.

Here's the scenario.

You are working in a lab and have to heat a solution with a burner for exactly 30 minutes. After a while you ask your lab partner to check on it. They tell you one of the following sentences.

A: The burner was on for 30 minutes

B: The burner has been on for 30 minutes.

Here's the scenario

A: The burner was on for 30 minutes

B: The burner has been on for 30 minutes.

One of these means you should rush to turn off the burner right now! Can you tell the difference between these sentences and explain why you should be worried?

What are the differences between sentence A and B?

A: The burner was on for 30 minutes.

This means that the burner was on for 30 minutes and was then turned off. It was not on for longer than those 30 minutes.

B: The burner has been on for 30 minutes.

This means that the burner has been on for at least 30 minutes and is still on. It carries on into the moment of speaking.

Let's practise

For the following sentences. Please indicate whether the action is still ongoing or finished. Simply answer either A or B for each sentence.

Mr ten Lohuis has taught us about lab safety for a year

1. Ongoing
2. Finished

I wrote part of the lab journal yesterday.

1. Ongoing
2. Finished

The Ph value rose a lot.

1. Ongoing
2. Finished

The power outage has lasted for three hours.

1. Ongoing
2. Finished

Let's take it a step further

For the next few sentences, complete the sentence to tell the reader whether it's an ongoing or finished process.

The sample ___ in the freezer for a day.
[to be - ongoing]

She ___ the ovens this morning
[to clean - finished]

Step 1

Write a sentence describing one of the things you do in your lab classes. Make sure to decide whether the action is ongoing or finished. Think of the previous examples and make your own sentence.

Step 2

After writing your sentence, exchange your work with a classmate. Check if you can understand each others sentence and if you can tell whether your partner's process is finished or ongoing.