Passive vs Active voice

Here's the difference and why. Recognize that I am coming to this not as a grammarian but as a fiction writer who blogs and manages content for my day job. So while both areas should have perfect grammar, they both have emphases which a standard grammarian might not see or think of note.

Active voice keeps the actor in the spotlight. E. g. I walked the dog. Although the dog and I are both living beings, I'm clearly the one in control. I'm the actor. I am the subject of the sentence. The predicate is the rest of it.

In contrast, consider: The dog was walked by me. Here, the subject of the sentence is not as clear. I'm still the actor, but by shoving the actor to the end of the sentence, it gives everything a passive feel of less conviction. The act is the same and the sentences have the same meaning. But the second one feels more weasel-y, if you get what I mean.

But! Consider uses for passive voice, which is a perfectly good way to write. In fiction writing, a subordinate person or a captive is a great character to go all passive voice on. The slave was bought by the master vs. The master bought the slave. Again, they mean the same, but the former emphasizes the slave's powerlessness better than the latter. But if you want to emphasize the master's power instead, then active voice works better.

I edit and beta read for other indie writers and I once edited an adventure story where it was a festival of passive voice. So here was a hero in the mold of Indiana Jones, yet everything was The gun was fired by him and The decision was made by him, etc. By using that format, it gutted the story and made what should have been an active, powerful character into a shadow of what he could have been. He fired the gun. He made the decision. Both of those sentences imply power and conviction. The meaning does not change, but active voice in that instance made for a far better story.

Another use of passive voice is in public relations. Consider We made mistakes versus Mistakes were made. The second sentence implies two unspoken words -- by us. E. g. Mistakes were made by us. But by dropping those final two words and using passive voice, it evokes a feeling that the mistakes were out of our control, whereas the active voice squarely takes responsibility for the errors. Both are acknowledgments of fault, yet the passive form allows for the possibility that the errors were beyond what we did, said, thought, paid for, etc.

Both forms are correct. And they both have their places. Usually, active voice will be better, but mind the exceptions I've outlined, above. Happy writing!

There is a preference for using the active voice as it tends to be clearer, less wordy, and more direct. There are occasions when the passive voice is acceptable, however. Actually I'd prefer something like this:
"In my talk, I will concentrate on our company structure."

I disagree with your teacher. I think the first sentence is awkward. People concentrate. A "talk" doesn't concentrate. You are doing the concentrating, you should be the subject of the sentence.

If you want to use the active voice (which is probably a good idea), you should write

I will concentrate my talk on our company structure.

Other than that, I think the second sentence is better than the first because it doesn't anthropomorphize the "talk".

Thanks a lot!